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Document and Entity Information - USD ($)	12 Months Ended
Document and Entity Information - USD ($)	Dec. 31, 2017	Mar. 12, 2018	Jun. 30, 2017
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2017
Document Fiscal Year Focus	2017
Document Fiscal Period Focus	FY
Trading Symbol	PIRS
Entity Registrant Name	PIERIS PHARMACEUTICALS, INC.
Entity Central Index Key	0001583648
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Smaller Reporting Accelerated Filer
Entity Common Stock, Shares Outstanding		53,855,371
Entity Public Float			$ 184,955,062

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 37,878	$ 29,356
Short term investments	34,751	0
Accounts receivable	15,546	57
Prepaid expenses and other current assets	1,615	3,260
Total current assets	89,790	32,673
Property and equipment, net	4,034	2,264
Long term investments	9,922	0
Other non-current assets	130	126
Total assets	103,876	35,063
Current liabilities:
Accounts payable	2,452	2,386
Accrued expenses and other current liabilities	6,170	3,719
Deferred revenues, current portion	37,153	2,275
Total current liabilities	45,775	8,380
Deferred revenue, net of current portion	46,542	1,409
Other long-term liabilities	37	47
Total liabilities	92,354	9,836
Stockholders’ equity:
Preferred stock, $0.001 par value per share, 10,000,000 shares authorized and 4,963 and 4,963 issued and outstanding at December 31, 2017 and December 31, 2016	0	0
Common stock, $0.001 par value per share, 300,000,000 shares authorized and 45,017,062 and 43,058,827 issued and outstanding at December 31, 2017 and December 31, 2016	45	43
Additional paid-in capital	136,484	129,350
Accumulated other comprehensive loss	(4,695)	(1,501)
Accumulated deficit	(120,312)	(102,665)
Total stockholders’ equity	11,522	25,227
Total liabilities and stockholders’ equity	$ 103,876	$ 35,063

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Dec. 31, 2017	Dec. 31, 2016
Preferred stock
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	4,963	4,963
Preferred stock, shares outstanding	4,963	4,963
Common stock
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized	300,000,000	300,000,000
Common stock, shares issued	45,017,062	43,058,827
Common stock, outstanding	45,017,062	43,058,827

CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Income Statement [Abstract]
Revenue	$ 25,275	$ 5,831
Operating expenses
Research and development	22,285	19,699
General and administrative	17,584	8,891
Total operating expenses	39,869	28,590
Loss from operations	(14,594)	(22,759)
Interest income	152	2
Other (expense) income, net	(2,102)	120
Loss before income taxes	(16,544)	(22,637)
Provision for income tax	1,103	162
Net loss	(17,647)	(22,799)
Other comprehensive income/(loss) components:
Foreign currency translation	(2,374)	(229)
Unrealized loss on available-for-sale securities	(820)	0
Comprehensive loss	$ (20,841)	$ (23,028)
Net loss per share
Basic and diluted (in dollars per share)	$ (0.40)	$ (0.55)
Weighted average number of common shares outstanding
Basic and diluted (in shares)	43,931	41,713

CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Convertible series A preferred shares	Common Shares	Additional paid-in capital	Accumulated other comprehensive loss	Accumulated deficit
Balance (in shares) at Dec. 31, 2015		0	39,833,000
Balance at Dec. 31, 2015	$ 31,128	$ 0	$ 40	$ 112,227	$ (1,273)	$ (79,866)
Increase (Decrease) in Stockholders' Equity
Net loss	(22,799)					(22,799)
Foreign currency translation adjustment	(229)				(229)
Unrealized losses on investments	0
Stock based compensation expense	1,905			1,905
Issuance of common and preferred stock, net of offering costs (in shares)		5,000	3,226,000
Issuance of common and preferred stock, net of offering costs	15,221		$ 3	15,218
Issuance of common stock resulting from exercise of stock options (in shares)			0
Issuance of common stock resulting from exercise of warrants (in shares)			0
Balance (in shares) at Dec. 31, 2016		5,000	43,059,000
Balance at Dec. 31, 2016	25,227	$ 0	$ 43	129,350	(1,501)	(102,665)
Increase (Decrease) in Stockholders' Equity
Net loss	(17,647)					(17,647)
Foreign currency translation adjustment	(2,374)				(2,374)
Unrealized losses on investments	(820)				(820)
Stock based compensation expense	3,046			3,046
Issuance of common stock resulting from exercise of stock options (in shares)			453,209
Issuance of common stock resulting from exercise of stock options	781			781
Issuance of common stock resulting from exercise of warrants (in shares)			1,505,026
Issuance of common stock resulting from exercise of warrants	3,309		$ 2	3,307
Balance (in shares) at Dec. 31, 2017		5,000	45,017,000
Balance at Dec. 31, 2017	$ 11,522	$ 0	$ 45	$ 136,484	$ (4,695)	$ (120,312)

CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY (Parenthetical) $ in Thousands	Dec. 31, 2016 USD ($)
Statement of Stockholders' Equity [Abstract]
Offering costs	$ 1,279

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Operating activities:
Net loss	$ (17,647)	$ (22,799)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Depreciation	369	361
Stock-based compensation	3,046	1,905
Other non-cash transactions	293	49
Foreign currency re-measurement loss/(gain)	(156)	0
Changes in operating assets and liabilities:
Accounts receivable	(14,469)	(59)
Prepaid expenses and other assets	1,900	(1,020)
Deferred revenue	74,378	3,752
Accounts payable	(332)	1,360
Accrued expenses and other current liabilities	2,060	2,063
Net cash provided by (used in) operating activities	49,754	(14,388)
Investing activities:
Purchase of property and equipment	(1,950)	(560)
Purchase of investments	(43,925)	0
Net cash used in investing activities	(45,875)	(560)
Financing activities:
Proceeds from exercise of options	781	0
Proceeds from exercise of warrants	3,309	0
Issuance of Common and Preferred Stock, net of issuance costs	0	15,221
Net cash provided by financing activities	4,090	15,221
Effect of exchange rate change on cash and cash equivalents	553	(267)
Net increase in cash and cash equivalents	8,522	6
Cash and cash equivalents at beginning of year	29,356	29,350
Cash and cash equivalents at end of year	37,878	29,356
Supplemental cash flow disclosures:
Cash paid for income taxes	0	162
Net unrealized loss on investments	820	0
Property and equipment included in accounts payable	$ 114	$ 22

Corporate Information	12 Months Ended
Corporate Information	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Corporate Information	Corporate Information Pieris Pharmaceuticals, Inc., was founded in May 2013, and acquired all interest in Pieris GmbH (formerly Pieris AG, a German company which was founded in 2001) in December 2014. Pieris Pharmaceuticals, Inc. and its consolidated subsidiaries (collectively “Pieris” or the “Company”) is a clinical-stage biopharmaceutical company that discovers and develops Anticalin based drugs to target validated disease pathways in a unique and transformative way. Pieris' corporate headquarters is located in Boston, MA and its research facility is located in Freising-Weihenstephan, Germany. The Company’s pipeline includes, among other programs, an immuno-oncology multispecific tailored for the tumor micro-environment, an inhaled Anticalin to treat uncontrolled asthma, and a half-life-optimized Anticalin to treat anemia. The Company’s core Anticalin technology and platform was developed in Germany, and the Company has partnership arrangements with major multi-national pharmaceutical companies headquartered in the U.S., Europe, Japan, and with regional pharmaceutical companies headquartered in India. As of December 31, 2017, the Company had cash, cash equivalents and investments of $82.6 million. Including the $47.3 million of net proceeds, after expenses, from the sale of common stock in February 2018, and the $30.0 million upfront fee received in March 2018 in connection with a strategic partnership agreement signed in February 2018 (See Note 13 - Subsequent events), the Company expects that its existing cash, cash equivalents, and investments, are sufficient to support operating expenses and capital expenditure requirements into the middle of 2020.

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2017

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

Basis of Consolidation

The accompanying consolidated financial statements of Pieris Pharmaceuticals, Inc. and its wholly owned subsidiaries were prepared in accordance with accounting principles generally accepted in the United States (“U.S. GAAP”). The consolidated financial statements include the accounts of all subsidiaries. All intercompany balances and transactions have been eliminated.

Use of Estimates

The preparation of the financial statements in accordance with U.S. GAAP requires management to make estimates, judgments, and assumptions that affect the reported amounts of assets, liabilities, revenues and expenses and the related disclosures at the date of the financial statements and during the reporting period. Significant estimates are used for, but are not limited to, revenue recognition; deferred tax assets, deferred tax liabilities and valuation allowances; fair value of stock options and various accruals. Management evaluates its estimates on an ongoing basis. Actual results and outcomes could differ materially from management’s estimates, judgments, and assumptions.

Foreign Currency Translation

The financial statements of Pieris’ foreign subsidiaries are translated from local currency into reporting currency, which is U.S. dollars, using the current exchange rate at the balance sheet date for assets and liabilities, and the weighted average exchange rate prevailing during the period for revenues and expenses. The functional currency for Pieris’ foreign subsidiaries is considered to be the local currency for each entity and, accordingly, translation adjustments for these subsidiaries are included in accumulated other comprehensive loss within stockholders’ equity.

Realized and unrealized gains and losses resulting from foreign currency transactions denominated in currencies other than the functional currency are reflected as other (expense) income, net in the consolidated statements of operations. Foreign currency gains and losses on available-for-sale investment transactions are recorded to other comprehensive income on our balance sheet per Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“ASC”) Topic 830, Foreign Currency Matters.

Cash, Cash Equivalents and Investments

The Company determines the appropriate classification of its investments at the time of purchase. All liquid investments with original maturities of 90 days or less from the purchase date are considered to be cash equivalents. The Company’s current and non-current investments are comprised of money market, asset backed securities, government treasuries, and corporate bonds that are classified as available-for-sale in accordance with FASB ASC Topic 320, Investments—Debt and Equity Securities. The Company classifies investments available to fund current operations as current assets on its balance sheets. Investments are classified as non-current assets on the balance sheets if (i) the Company has the intent and ability to hold the investments for a period of at least one year and (ii) the contractual maturity date of the investments is greater than one year.

Available-for-sale investments are recorded at fair value, with unrealized gains or losses included in accumulated other comprehensive loss on the Company’s balance sheets. Realized gains and losses are determined using the specific identification method and are included as a component of interest income. There were no realized gains or losses recognized for the years ended December 31, 2017 and 2016, respectively.

The Company reviews investments for other-than-temporary impairment whenever the fair value of an investment is less than the amortized cost and evidence indicates that an investment’s carrying amount is not recoverable within a reasonable period of time. To determine whether an impairment is other-than temporary, the Company considers its intent to sell, or whether it is more likely than not that the Company will be required to sell the investment before recovery of the investment’s amortized cost basis. Evidence considered in this assessment includes reasons for the impairment, the severity and the duration of the impairment, and changes in value subsequent to period end. As of December 31, 2017, there were no investments with a fair value that was significantly lower than the amortized cost basis or any investments that had been in an unrealized loss position for a significant period.

Concentration of Credit Risk and Off-Balance Sheet Risk

The Company has no financial instruments with off‑balance sheet risk such as foreign exchange contracts, option contracts, or other foreign hedging arrangements. Financial instruments that subject Pieris to concentrations of credit risk include cash and cash equivalents, investments, and accounts receivable. The Company’s cash, cash equivalents, and investments are held in accounts with financial institutions that management believes are creditworthy. The Company’s investment policy includes guidelines on the quality of the institutions and financial instruments and defines allowable investments that the Company believes minimizes the exposure to concentration of credit risk. These amounts, at times, may exceed federally insured limits. The Company has not experienced any credit losses in such accounts and does not believe it is exposed to any significant credit risk on these funds. Accounts receivable primarily consist of amounts due under strategic partnership and other license agreements with major multi-national pharmaceutical companies for which the Company does not obtain collateral.

Fair Value Measurement

The Company is required to disclose information on all assets and liabilities reported at fair value that enables an assessment of the inputs used in determining the reported fair values. FASB ASC Topic 820, Fair Value Measurement and Disclosures, (“ASC 820”) established a hierarchy of inputs used in measuring fair value that maximizes the use of observable inputs and minimizes the use of unobservable inputs by requiring that the observable inputs be used when available. Observable inputs are inputs that market participants would use in pricing the financial instrument based on market data obtained from sources independent of the Company. Unobservable inputs are inputs that reflect the Company’s assumptions about the inputs that market participants would use in pricing the financial instrument and are developed based on the best information available in the circumstances. The fair value hierarchy applies only to the valuation inputs used in determining the reported or disclosed fair value of the financial instruments and is not a measure of the investment credit quality. Fair value measurements are classified and disclosed in one of the following three categories:


•	Level 1 inputs are quoted prices in active markets for identical assets or liabilities that the reporting entity has the ability to access at the measurement date.


•	Level 2 utilizes quoted market prices in markets that are not active, broker or dealer quotations, or alternative pricing sources with reasonable levels of price transparency.


•	Level 3 inputs are unobservable inputs for the asset or liability in which there is little, if any, market activity for the asset or liability at the measurement date.

To the extent that valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair value requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized in Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement.

Financial instruments measured at fair value on a recurring basis include cash equivalents and investments (Note 4).

An entity may elect to measure many financial instruments and certain other items at fair value at specified election dates. Subsequent unrealized gains and losses on items for which the fair value option has been elected will be reported in net loss. The Company did not elect to measure any additional financial instruments or other items at fair value.

Fair Values of Financial Instruments

The fair value of cash, accounts receivable, and accounts payable approximates the carrying value of these financial instruments because of the short-term nature of any maturities. The Company determines the estimated fair values of other financial instruments, using available market information and valuation methodologies, primarily input from independent third party pricing sources.

Accounts Receivable

Accounts receivable are recorded net of allowances for doubtful accounts and represent amounts due from third parties, strategic partners, and other license agreement counterparties. The Company monitors and evaluates collectability of receivables on an ongoing basis and considers whether an allowance for doubtful accounts is necessary. The Company determined that no such reserve is needed as of December 31, 2017 and 2016. Historically, Pieris has not had collectability issues.

Property and Equipment

Property and equipment are recorded at acquisition cost, less accumulated depreciation and impairment. Depreciation on property and equipment is calculated using the straight-line method over the remaining estimated useful lives of the assets. Maintenance and repairs to these assets are charged to expenses as occurred. The estimated useful life of the different groups of property and equipment is as follows:



Asset Classification		Estimated useful life (in years)
Leasehold improvements		shorter of useful life or remaining life of the lease
Laboratory equipment		10 - 14
Office and computer equipment		3 - 13

Impairment of Long-lived Assets

Pieris reviews its long-lived assets to be held and used for impairment whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. Pieris evaluates the realizability of its long-lived assets based on profitability and cash flow expectations for the related asset. Any write-downs are treated as permanent reductions in the carrying amount of the assets. Pieris believes that, as of each of the balance sheets presented, none of Pieris’ long-lived assets were impaired.

Revenue Recognition

Pieris has entered into several licensing and development agreements with collaboration partners for the development of Anticalin® therapeutics against a variety of targets in diseases and conditions. The terms of these agreements contain multiple elements and deliverables, which may include: (i) licenses, or options to obtain licenses, to Pieris’ Anticalin technology and (ii) research and development activities to be performed on behalf of the collaborative partner. Payments to Pieris under these agreements may include upfront fees (which include license and option fees), payments for research and development activities, payments based upon the achievement of certain milestones and royalties on product sales. There are no performance, cancellation, termination or refund provisions in any of the arrangements that could result in material financial consequences to Pieris. Pieris follows the provisions of the FASB ASC Topic 605-25, Revenue Recognition—Multiple-Element Arrangements ("ASC 605-25") and FASB ASC Topic 605-28, Revenue Recognition—Milestone Method ("ASC 605-28") in accounting for these agreements.

Multiple-Element Arrangements

When evaluating multiple-element arrangements, Pieris identifies the deliverables included within the agreement and evaluates which deliverables represent separate units of accounting based on whether the delivered element has stand-alone value to the customer or if the arrangement includes a general right of return for delivered items.

The consideration received is allocated among the separate units of accounting using the relative selling price method, and the applicable revenue recognition criteria are applied to each of the separate units of accounting. Pieris uses the best estimate of selling price (“BESP”) methodology to estimate the selling price for each deliverable and unit of accounting because Pieris does not have vendor specific objective evidence (“VSOE”) or third-party evidence (“TPE”) of selling price for these deliverables. To determine the estimated selling price of a deliverable, Pieris considers market conditions as well as entity-specific factors, including those factors contemplated in negotiating the agreements, terms of previous collaborative agreements, similar agreements entered into by third parties, market opportunity, estimated development costs, probability of success, and the time needed to commercialize a product candidate pursuant to the license. In validating Pieris’ BESP, Pieris evaluates whether changes in the key assumptions used to determine the BESP will have a significant effect on the allocation of arrangement consideration among multiple deliverables.

Multiple element arrangements, such as license and development arrangements, are analyzed to determine whether the deliverables, which often include licenses and performance obligations such as research and development services and steering committee services, can be separated or whether they must be accounted for as a combined unit of accounting in accordance with U.S. GAAP. The Company recognizes the arrangement consideration allocated to licenses as revenue upon delivery of the license only if the license has stand-alone value. If the license is considered not to have stand-alone value, the license would then be combined with other undelivered elements into a combined unit of accounting and the license payments and payments for performance obligations would be recognized as revenue when the revenue recognition criteria have been satisfied for the last deliverable within the unit of accounting. In the case of combined units of accounting that include delivered licenses and undelivered services to be provided over time, revenue would be recognized over the estimated period during which services will be provided. For units of accounting that include licenses to be delivered upon satisfactory completion of certain research services, revenue is deferred until the license is delivered and the performance obligation is satisfied.

If the Company is involved in a steering committee, as part of a multiple element arrangement, it assesses whether its involvement constitutes a performance obligation or a right to participate. When steering committee services are determined to be performance obligations, the Company determines the fair value to be allocated to this deliverable and recognize the revenue over the expected term of the development period of the products. Otherwise, the fair value for participation is combined with other research services or performance obligations and is recognized over the term which the Company expects to complete its aggregate performance obligations.

The Company recognizes arrangement consideration allocated to each unit of accounting when all of the revenue recognition criteria in ASC 605-25 are satisfied for that particular unit of accounting. For each unit of accounting, the Company must determine the period over which the performance obligations will be performed and revenue will be recognized. If there is no discernible pattern of performance or objectively measurable performance measures do not exist, then the Company recognizes revenue under the arrangement on a straight-line basis over the period the Company is expected to complete its performance obligations. Conversely, if the pattern of performance over which the service is provided to the customer can be determined and objectively measurable performance measures exist, then the Company recognizes revenue under the arrangement using the proportional performance method. Revenue recognized is limited to the lesser of the cumulative amount of payments received or the cumulative amount of revenue earned as of the period ending date.

Significant management judgment is required in determining the level of effort required under an arrangement and the period over which the Company is expected to complete its performance obligations under an arrangement.

The accounting treatment for options granted to collaborators is dependent upon the nature of the option granted to the collaborative partner. Options are considered substantive if, at the inception of an agreement, Pieris is at risk as to whether the collaborative partner will choose to exercise the option(s) to secure additional goods or services. Factors that are considered in evaluating whether options are substantive include the overall objective of the arrangement, benefit the collaborator might obtain from the agreement without exercising the options, cost to exercise the options relative to the total upfront consideration, and additional financial commitments or economic penalties imposed on the collaborator as a result of exercising the options.

In arrangements where options to obtain additional deliverables are considered substantive, Pieris determines whether the optional licenses are priced at a significant and incremental discount. If the prices include a significant and incremental discount, the option is considered a deliverable in the arrangement. However, if not priced at a discount, the option is not considered a deliverable in the arrangement. When a collaborator exercises an option considered to be at a significant and incremental discount to acquire an additional license, the exercise fee that is attributed to the additional license and any incremental discount allocated at inception are recognized in a manner consistent with the treatment of up-front payments for licenses (i.e., license and research services). In the event an option expires un-exercised, any incremental discounts deferred at the inception of the arrangement are recognized into revenue upon expiration. For options that are non-substantive, the additional licenses to which the options pertain are considered deliverables upon inception of the arrangement; Pieris applies the multiple-element revenue recognition criteria to determine accounting treatment.

Payments or reimbursements resulting from Pieris’ research and development efforts in multi-element arrangements, in which Pieris’ research and development efforts are considered to be a deliverable, are included in allocable consideration and allocated to the units of accounting. These reimbursements are recognized as the services are performed and are presented on a gross basis, so long as there is persuasive evidence of an arrangement, the fee is fixed or determinable, and collection of the related receivable is reasonably assured. Revenue recognized cannot exceed the amount that has been earned and has been billed or is currently billable. Amounts received prior to satisfying the above revenue recognition criteria are recorded as deferred revenue in the accompanying balance sheets.

Milestone Payments and Royalties

At the inception of each agreement that includes milestone payments, Pieris evaluates whether each milestone is substantive and at risk to both parties on the basis of the contingent nature of the milestone. This evaluation includes an assessment of whether: (a) the consideration is commensurate with either (1) the entity’s performance to achieve the milestone, or (2) the enhancement of the value of the delivered item(s) as a result of a specific outcome resulting from the entity’s performance to achieve the milestone, (b) the consideration relates solely to past performance and (c) the consideration is reasonable relative to all of the deliverables and payment terms within the arrangement. Pieris evaluates factors such as the scientific, regulatory, commercial and other risks that must be overcome to achieve the respective milestone, the level of effort and investment required to achieve the respective milestone and whether the milestone consideration is reasonable relative to all deliverables and payment terms in the arrangement in making this assessment.

Pieris aggregates milestones into four categories (i) research milestones, (ii) development milestones, (iii) commercial milestones and (iv) sales milestones. Research milestones are typically achieved upon reaching certain success criteria as defined in each agreement related to developing an Anticalin protein against the specified target. Development milestones are typically reached when a compound reaches a defined phase of clinical research or passes such phase, or upon gaining regulatory approvals. Commercial milestones are typically achieved when an approved pharmaceutical product reaches the status for commercial sale, including regulatory approval. Sales milestones are certain defined levels of net sales by the licensee, such as when a product first achieves global sales or annual sales of a specified amount.

For revenues from research, development, and commercial milestone payments, if the milestones are deemed substantive and the milestone payments are nonrefundable, such amounts are recognized entirely upon successful accomplishment of the milestones, assuming all other revenue recognition criteria are met. Milestones that are not considered substantive are accounted for as contingent revenue and will be recognized when achieved to the extent the Company has no remaining performance obligations under the arrangement. Revenues from sales milestone payments are accounted for as royalties and are recorded as revenue upon achievement of the milestone, assuming all other revenue recognition criteria are met. Royalty payments are recognized in revenues based on the timing of royalty payments earned in accordance with the agreements, which typically is the period when the relevant sales occur, assuming all other revenue recognition criteria are met.

Research and Development

Research and development expenses are charged to the statement of operations as incurred. Research and development expenses are comprised of costs incurred in performing research and development activities, including salaries and benefits, facilities costs, pre-clinical and clinical costs, contract services, consulting, depreciation and amortization expense, and other related costs. Costs associated with acquired technology, in the form of upfront fees or milestone payments, are charged to research and development expense as incurred.

Incremental direct cost

Incremental direct costs incurred related to the acquisition or origination of a customer contract in a transaction that results in the deferral of revenue are recorded to the statement of operations as incurred.

Income Taxes

The Company applies ASC Topic 740 Income Taxes, which established financial accounting and reporting requirements for the effects of income taxes that result from the Company’s activities during the current and preceding years. Deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases, and operating losses and tax credit carry forwards. Deferred tax assets and liabilities are measured using enacted statutory tax rates expected to apply to taxable income in the jurisdictions and years in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in income in the period that includes the enactment date. Where the Company determines that it is more likely than not that some portion or all of the deferred tax assets will not be realized in the future, the deferred tax assets are reduced by a valuation allowance. The Company records interest related and penalties related to uncertain tax positions as part of income tax expense.

Stock-based Compensation

Pieris measures share-based payments in accordance with ASC Topic 718, Stock Compensation. Pieris records its stock-based compensation expense over the requisite service period. Determining the appropriate fair value model and related assumptions requires judgment, including estimating share price volatility and expected terms of the awards. For employee options, the fair value measurement date is generally on the date of grant and the related compensation expense is recognized on a straight-line basis over the requisite period of the awards, less expense for actual forfeitures.

The Company uses the Black-Scholes option pricing model to determine the estimated fair value for stock-based awards. Option-pricing models require the input of various subjective assumptions, including the option’s expected life, expected dividend yield, price volatility, risk free interest rate and forfeitures of the underlying stock. Due to the limited operating history of the Company as a public entity and a lack of company specific historical and implied volatility data, the Company has based its estimate of expected volatility on the historical volatility of a group of similar companies that are publicly traded. When selecting these public companies on which it has based its expected stock price volatility, the Company selected companies with comparable characteristics to it, including enterprise value, risk profiles, position within the industry, and with historical

share price information sufficient to meet the expected term of the stock-based awards. The Company computes historical volatility data using the daily closing prices for the selected companies’ shares during the equivalent period of the calculated expected term of the stock-based awards. The Company will continue to apply this process until a sufficient amount of historical information regarding the volatility of its own stock price becomes available.

Due to the lack of Company specific historical option activity, the Company has estimated the expected term of its employee stock options using the “simplified” method, whereby, the expected term equals the arithmetic average of the vesting term and the original contractual term of the option. The expected term for non-employee awards is the remaining contractual term of the option. The risk-free interest rates are based on the U.S. Treasury securities with a maturity date commensurate with the expected term of the associated award. The Company has never paid, and does not expect to pay dividends in the foreseeable future.

The Company early adopted ASU 2016-09 Compensation - Stock Compensation (Topic 718) as of January 1, 2016. In connection with the early adoption, the Company elected an accounting policy to record forfeitures as they occur. There was no material financial statement impact upon adoption. ASU 2016-09 also provides that companies no longer record excess tax benefits or certain tax deficiencies in additional paid-in capital. Instead, all excess tax benefits and tax deficiencies are recorded as income tax expense or benefit in the Company's statement of operations and comprehensive loss. There was no financial statement impact of adopting this provision of ASU 2016-09 as there were no options previously exercised. As such, the adoption of this standard did not have a material impact on the financial statements. For the years ended December 31, 2017 and 2016, the Company did not record an income statement benefit for excess tax benefits as a valuation allowance is also required on these amounts.

Contingencies

Accruals are recorded for loss contingencies when it is probable that a liability has been incurred and the amount of the related loss can be reasonably estimated. Pieris evaluates, on a quarterly basis, developments in legal proceedings and other matters that could cause an increase or decrease in the amount of the liability that has been accrued previously. Considering facts known at the time of the assessment, Pieris determines whether potential losses are considered reasonably possible or probable and whether they are estimable. Based upon this assessment, Pieris carries out an evaluation of disclosure requirements and considers possible accruals in the financial statements.

Segment Reporting

Operating segments are identified as components of an enterprise where separate discrete financial information is available for evaluation by the chief operating decision maker in making decisions on how to allocate resources and assess performance. Pieris operates as a single segment dedicated to the discovery and development of biotechnological applications and the Company’s chief operating decision maker (“CODM”) makes decisions based on the Company as a whole. The Company has determined that its CODM is its Chief Executive Officer.

Earnings per Share

Basic earnings per share attributable to common stockholders is calculated by dividing net loss attributable to common stockholders by the weighted average shares outstanding during the period, without consideration for common stock equivalents.

Diluted earnings per share attributable to common stockholders is calculated by adjusting weighted average shares outstanding for the dilutive effect of common stock equivalents outstanding for the period, determined using the treasury-stock and if-converted methods. For purposes of the diluted net loss per share attributable to common stockholders' calculation, preferred stock, stock options, unvested restricted stock, and warrants are considered to be common stock equivalents but have been excluded from the calculation of diluted net loss per share attributable to common stockholders, as their effect would be anti-dilutive for all periods presented. Therefore, basic and diluted net loss per share were the same for all periods presented.

Recent Accounting Pronouncements

Standards not yet adopted

In May 2014, the FASB issued Accounting Standard Update (“ASU”) No. 2014-09, Revenue from Contracts with Customers (Topic 606) (“ASU 2014-09”). Subsequently, the FASB also issued ASU 2015-14, Revenue from Contracts with Customers (Topic 606) , which adjusted the effective date of ASU 2014-09; ASU No. 2016-08, Revenue from Contracts with Customers (Topic 606): Principal versus Agent Considerations (Reporting Revenue Gross versus Net), which amends the principal-versus-agent implementation guidance and illustrations in ASU 2014-09; ASU No. 2016-10, Revenue from Contracts with Customers (Topic 606): Identifying Performance Obligations and Licensing, which clarifies identifying performance obligation and licensing implementation guidance and illustrations in ASU 2014-09; and ASU No. 2016-12, Revenue from Contracts with Customers (Topic 606): Narrow-Scope Improvements and Practical Expedients, which addresses implementation issues and is intended to reduce the cost and complexity of applying the new revenue standard in ASU 2014-09 (collectively, the “Revenue ASUs”).

The Revenue ASUs provide an accounting standard for a single comprehensive model for use in accounting for revenue arising from contracts with customers and supersedes most current revenue recognition guidance. The accounting standard is effective for public emerging growth companies ("EGC"), like Pieris, for interim and annual periods beginning after December 15, 2018, with an option to early adopt for interim and annual periods beginning after December 15, 2017. The guidance permits two methods of adoption: retrospectively to each prior reporting period presented (the full retrospective method), or retrospectively with the cumulative effect of initially applying the guidance recognized at the date of initial application (the modified retrospective method). The Company is in the process of determining the date and method of adoption and the impact of the Revenue Recognition ASUs on its financial statements.

In February 2016, the FASB issued ASU No. 2016-2, Leases (Topic 842) ("ASU 2016-2"). Under the amendments in ASU 2016-2, lessees will be required to recognize (i) a lease liability, which is a lessees obligation to make lease payments arising from a lease, measured on a discounted basis; and (ii) a right-of-use asset, which is an asset that represents the lessee’s right to use, or control the use of, a specified asset for the lease term for all leases (with the exception of short-term leases) at the commencement date. This guidance is effective for fiscal years beginning after December 15, 2019 including interim periods within those fiscal years. Early adoption is permitted. The Company is currently evaluating the potential impact the adoption of this standard will have on its financial statements and related disclosures.

In May 2017, the FASB issued ASU No. 2017-09, Compensation - Stock compensation (Topic 718) (“ASU 2017-09”). The amendments in this update provide guidance about which changes to the terms or conditions of a share-based payment award require an entity to apply modification accounting. This ASU will be effective for the Company’s fiscal year beginning January 1, 2018, and the Company is not expecting a material impact the adoption will have on its financial statements.

Pieris has considered other recent accounting pronouncements and concluded that they are either not applicable to the business, or that the effect is not expected to be material to the unaudited condensed consolidated financial statements as a result of future adoption.

Revenue

12 Months Ended

Dec. 31, 2017

Revenue from Contract with Customer [Abstract]

Revenue

General

The Company has not generated revenue from product sales. The Company has generated revenue pursuant to (i) license and collaboration agreements, which include upfront payments for licenses or options to obtain licenses, payments for research and development services and milestone payments, and (ii) government grants. During the years ended December 31, 2017 and 2016, respectively, the Company recognized revenues as follows (in thousands):



	Years Ended December 31,
	2017		2016
License fees	$	11,285	$	2,736
Research and development services	1,403		1,440
Milestone payments	12,573		1,655
Other revenues	14		—
Total Revenue	$	25,275	$	5,831

During the years ended December 31, 2017 and 2016, respectively, the Company recognized revenue from the following strategic partnerships and other license agreements (in thousands):



	Years Ended December 31,
	2017		2016
AstraZeneca	$	19,769	$	—
Servier	1,907		—
Roche	3,516		4,080
Other	83		1,751
Total Revenue	$	25,275	$	5,831

Under the Company´s existing strategic partnerships and other license agreements, Pieris could receive the following potential milestone payments (in millions):



	Research, Development & Regulatory Milestones		Sales Milestones
AstraZeneca	$	1,111	$	960
Servier	1,040		942
Roche	290		123
Other	68		—
Total potential milestone payments	$	2,509	$	2,025

Strategic Partnerships and Other License Agreements

AstraZeneca AB

On May 2, 2017, Pieris entered into a License and Collaboration Agreement (“AstraZeneca Collaboration Agreement”), and a Non-Exclusive Anticalin Platform Technology License Agreement (the “License Agreement” and together with the AstraZeneca Collaboration Agreement, the “AstraZeneca Agreements”) with AstraZeneca AB (“AstraZeneca”), which became effective on June 10, 2017, following expiration of the waiting period under the Hart-Scott-Rodino Antitrust Improvements Act of 1976. Under the AstraZeneca Agreements the parties will advance several novel inhaled Anticalin proteins.

In addition to the Company’s lead inhaled drug candidate, PRS-060 (the “AstraZeneca Lead Product”), Pieris and AstraZeneca will also collaborate to progress four additional novel Anticalin proteins against undisclosed targets for respiratory diseases (the “AstraZeneca Collaboration Products” and together with the AstraZeneca Lead Product, the “AstraZeneca Products”). Pieris is responsible for advancing the AstraZeneca Lead Product through the Phase I trial, with the associated costs funded by AstraZeneca. The parties will collaborate thereafter to conduct a Phase IIa clinical trial in asthma patients, with AstraZeneca continuing to fund development costs. After completion of the Phase IIa trial, Pieris has the option to co-develop the AstraZeneca Lead Product and also has the option to co-commercialize the AstraZeneca Lead Product in the United States. For the four AstraZeneca Collaboration Products, Pieris will be responsible for the initial discovery of the novel Anticalin proteins, after which AstraZeneca will take the lead on continued development. Pieris has the option to co-develop two of these four AstraZeneca Collaboration Products beginning at a pre-defined preclinical stage and would also have the option to co-commercialize these two programs in the United States, while AstraZeneca will be responsible for development and commercialization of the other programs worldwide.

The term of the AstraZeneca Agreement ends upon the expiration of all of AstraZeneca’s payment obligations under such AstraZeneca Agreement. The AstraZeneca Collaboration Agreement may be terminated by AstraZeneca in its entirety for convenience beginning 12 months after its effective date upon 90 days’ notice or, if Pieris has obtained marketing approval for the marketing and sale of a product, a 180 days’ notice. Each program may be terminated at AstraZeneca’s option, and if any program is terminated by AstraZeneca, Pieris will have full rights to such program. The AstraZeneca Collaboration Agreement may also be terminated by AstraZeneca or Pieris for material breach upon 180 days’ notice of a material breach (or 30 days with respect to payment breach), provided that the applicable party has not cured such breach by the permitted cure period (including an additional 180 days if the breach is not susceptible to cure during the initial 180-day period) and dispute resolution procedures specified in the applicable AstraZeneca Agreement have been followed. The AstraZeneca Collaboration Agreement may also be terminated due to the other party’s insolvency and may in certain instances be terminated on a product-by-product and/or country-by-country basis. Each party may also terminate the agreement if the other party challenges the validity of patents related to certain intellectual property licensed under the AstraZeneca Agreement, subject to certain exceptions for infringement suits, acquisitions and newly-acquired licenses. The License Agreement will terminate upon termination of the AstraZeneca Collaboration Agreement, on a product-by-product and/or country-by-country basis.

At inception, AstraZeneca is granted the following licenses: (i) research and development license for the AstraZeneca Lead Product, (ii) commercial license for the AstraZeneca Lead Product, (iii) individual research licenses for each of the four AstraZeneca Collaboration Products, (iv) individual commercial licenses for each of the four AstraZeneca Collaboration Products, and (v) individual non-exclusive platform technology licenses for the AstraZeneca Lead Product and the four AstraZeneca Collaboration Products. AstraZeneca will be granted individual development licenses for each of the four AstraZeneca Collaboration Products upon completion of the initial discovery of Anticalin proteins.

The collaboration will be managed on an overall basis by a Joint Steering Committee (“JSC”) formed by an equal number of representatives from the Company and AstraZeneca. In addition to the JSC, the AstraZeneca Collaboration Agreement also requires each party to designate an Alliance Manager to facilitate communication and coordination of the Parties activities under that AstraZeneca Agreement, as well as requires participation of both parties on: (i) a Joint Development Committee (“JDC”) and (ii) a Commercialization Committee. The responsibilities of these committees vary, depending on the stage of development and commercialization of each Product.

Under the AstraZeneca Agreements, the Company received an upfront, non-refundable payment of $45.0 million. In addition, the Company will receive payments to conduct a Phase I trial for the AstraZeneca Lead Product. The Company is also eligible to receive research, development, commercial, sales milestone payments, and royalty payments. The Company may receive tiered royalties on sales of potential products commercialized by AstraZeneca and for co-developed products, gross margin share on worldwide sales equal dependent on Pieris’ level of committed investment.

The Company accounted for the AstraZeneca Agreements as a multiple element arrangement under ASC 605-25. The arrangement with AstraZeneca contains the following initial deliverables: (i) five non-exclusive platform technology licenses, (ii) research and development license for the AstraZeneca Lead Product, (iii) commercial license for the AstraZeneca Lead Product, (iv) development and manufacturing services for the AstraZeneca Lead Product, (v) technology transfer services for the AstraZeneca Lead Product, (vi) research services related to the AstraZeneca Lead Product, (vii) participation on each of the committees, (viii) four research licenses for the AstraZeneca Collaboration Products, (ix) four commercial licenses for the AstraZeneca Collaboration Products, and (x) research services for the AstraZeneca Collaboration Products. Additionally, as the development licenses on the four AstraZeneca Collaboration Products may be granted at a discount in the future, the Company determined such discounts be included as an element of the arrangement at inception.

Management considered whether any of the deliverables could be considered separate units of accounting. The Company determined that the licenses granted for the AstraZeneca Lead Product at the inception of the arrangement did not have standalone value from the research services related to the AstraZeneca Lead Product and the licenses granted for the AstraZeneca Collaboration Products did not have standalone value from the research services for the AstraZeneca Collaboration Products, due to the specific nature of the intellectual property and knowledge required to perform the services. The Company also determined that the licenses granted at the inception of the arrangement did have standalone value from the development and manufacturing services for the AstraZeneca Lead Product, but that the participation on the various committees did have standalone value as the development and manufacturing services and committee service could be performed by an outside party. The Company determined that the commercial licenses for the AstraZeneca Collaboration Products granted at the inception of the arrangement did not have standalone value from the development licenses for the AstraZeneca Collaboration Products as the company would not benefit from the commercial license without the ability to develop each product.

As a result, management concluded that there were eleven units of accounting at the inception of the AstraZeneca Agreements: (i) combined unit of accounting representing a non-exclusive platform technology license, research and development license, and commercial licenses for the AstraZeneca Lead Product and research services for the AstraZeneca Lead Product, (ii) combined unit of accounting representing development and manufacturing services, and technology transfer services for the AstraZeneca Lead Product, (iii) committee participation, (iv-vii) four units of accounting representing a combined non-exclusive platform technology license, research licenses, and research services for each AstraZeneca Collaboration Product, and (viii-xi) four units of accounting representing the combined commercial licenses granted for the AstraZeneca Collaboration Products and corresponding discounts on the development licenses granted for the AstraZeneca Collaboration Products upon the achievement of specified preclinical activities.

The Company determined that neither VSOE nor TPE is available for any of the units of accounting identified at the inception of the arrangement. Accordingly, the selling price of each unit of accounting was developed using management’s BESP. The Company developed the BESP for licenses and corresponding research services by applying a risk adjusted, net present value, estimate of future potential cash flow approach, which included the cost of obtaining research services at arm’s length from a third-party provider, as well as internal full time equivalent costs to support these services. The Company developed the BESP for development and manufacturing services, and technology transfer services for the AstraZeneca Lead Product using estimated internal and external costs to be incurred.

The Company developed the BESP for committee participation by using management’s best estimate of the anticipated participation hours multiplied by a market rate for comparable participants.

The Company developed the BESP for the commercial licenses and discounts granted on the development licenses by probability weighting multiple cash flow scenarios using the income approach.

Allocable arrangement consideration at inception is comprised of the $45.0 million upfront fee and the $8.2 million estimated development and manufacturing services to be reimbursed for the AstraZeneca Lead Product. The aggregate allocable consideration of $53.2 million is allocated among the separate units of accounting using the relative selling price method.

The amounts allocated to the unit of accounting for the AstraZeneca Lead Product and four units of accounting for the four AstraZeneca Collaboration Products will be recognized on a proportional performance basis as the activities are conducted over the life of the arrangement. The amounts allocated to the development and manufacturing services, and technology transfer services for the AstraZeneca Lead Product will be recognized on a proportional performance basis over the estimated term of development through Phase IIa trial. The amounts allocated to the participation on each of the committees will be recognized on a straight-line basis over the expected term of development of the AstraZeneca Lead Product and the AstraZeneca Collaboration Products. The term of performance at the inception of the arrangement is approximately five years. The amounts allocated to the commercial licenses and discounts on the development licenses granted in the future for the AstraZeneca Collaboration Products will be recognized upon delivery of each of the development licenses assuming all other revenue recognition criteria have been met. Additionally, the Company evaluated payments required to be made between both parties as a result of the shared development costs of the AstraZeneca Lead Product and the two AstraZeneca Collaboration Products for which Pieris has a co-development option. The Company will classify payments made as a reduction of revenue and will classify payments received as revenue, in the period they are earned.

Under the AstraZeneca Agreements the Company is eligible to receive various research, development, commercial, and sales milestones. Management determined certain of the research, development, and commercial milestones that may be received under the AstraZeneca Agreements are substantive when the Company is involved in the development and commercialization of the applicable AstraZeneca Products. Payment related to achievement of such milestones, if any, will be recognized as revenue when the milestone is achieved. Total potential substantive development milestones range from $72.2 million to $611.4 million, dependent on the Company’s decision, on a product-by-product basis, whether to co-develop the AstraZeneca Lead Product and AstraZeneca Collaboration Products. Research, development, and commercial, and sales milestones are deemed non-substantive if they are based solely on the performance of another party. Non-substantive milestones will be treated as contingent revenue and will be recognized when achieved to the extent the Company has no remaining performance obligations under the arrangement. Total potential non-substantive research, development, and commercial milestones range from $366.2 million to $1.1 billion. The Company may receive lower research, development, and commercial, milestones if the Company chooses to co-develop the AstraZeneca Lead Product and/or AstraZeneca Collaboration Products, depending on the level of co-development investment. Total potential sales milestones are up to $1.0 billion and will be recognized when earned, assuming all other revenue recognition revenue criteria have been met.

The Company will recognize royalty and gross margin share revenue in the period of sale of the related AstraZeneca Product, based on the underlying contract terms, provided that the reported sales are reliably measurable and the Company has no remaining performance obligations, assuming all other revenue recognition criteria are met.

The successful initiation of a Phase I study during the year ended December 31, 2017 resulted in a milestone achievement of $12.6 million, which was recorded as revenue in the respective period. As of December 31, 2017, there is $28.6 million and $16.3 million of deferred revenue and non-current deferred revenue, respectively, related to the AstraZeneca Agreements.

ASKA Pharmaceutical Co. Ltd.

On February 27, 2017 the Company entered into an Exclusive Option Agreement (the “Aska Agreement”) with ASKA Pharmaceutical Co., Ltd. (“Aska”) to grant Aska an option to acquire (1) a non-exclusive license to certain intellectual property rights associated with the Pieris’ Anticalin platform (“Licensed Platform IP”) and (2) an exclusive license to certain intellectual property rights specifically related to Pieris’ PRS-080 Anticalin protein (“Licensed Product IP”) in order to develop, manufacture, import, sale, export, and offer for sale and export any pharmaceutical formulation containing PRS-080, the Company’s PEGylated Anticalin protein targeting hepcidin (“Licensed Product”) in Japan and certain other Asian territories (“Licensed Territory”).

Pieris is obliged to use commercially reasonable efforts to complete the Phase IIa Study for PRS-080 and to submit to Aska, in writing, the final results of the study when available. Upon receipt, Aska will have 60 days to evaluate the results of the Phase IIa study (“Evaluation Period”). Aska agreed to notify Pieris, in writing, of its decision to exercise its option to acquire rights to the Licensed Product. If the Phase IIa Study meets the applicable success criteria and Aska fails to provide notification that it will exercise its option, Aska shall pay the Company an additional fee within thirty days of the end of the Evaluation Period (the “Break-Up Fee”). If Aska exercises the option, Aska and the Company will enter into a separate definitive arrangement governing the future development and commercialization activities.

The Company determined that the completed Phase IIa study represents the single deliverable (and the sole unit of account) under the Aska Arrangement for which an upfront payment of $2.75 million was received from Aska. While the completion of the Phase IIa trial requires the completion of a number of actions, the Company determined that the significance in value of the finalization of the data and evaluation of results of the Phase IIa study is the point at which revenue would be recognized. Therefore, no revenue was recognized in connection with this arrangement for the years ended December 31, 2017 and 2016, respectively. As of December 31, 2017, there is $3.1 million of current deferred revenue related to the Company’s option agreement with Aska.

Les Laboratoires Servier and Institut de Recherches Internationales Servier

On January 4, 2017, Pieris entered into a License and Collaboration Agreement (“Servier Collaboration Agreement”), and Non-Exclusive Anticalin Platform Technology Agreement (the “License Agreement” and together with the Servier Collaboration Agreement, the “Servier Agreements”) with Les Laboratoires Servier and Institut de Recherches Internationales Servier (collectively “Servier”) pursuant to which Pieris and Servier will initially pursue five bispecific therapeutic programs, led by the PRS-332 program (the “Lead Product”), a PD-1-targeting bispecific checkpoint inhibitor. Pieris and Servier will jointly develop PRS-332 and split commercial rights geographically, with Pieris retaining all commercial rights in the United States and Servier having commercial rights in the rest of the world. Each party is responsible for an agreed upon percentage of shared costs, as set forth in the budget for the joint development plan, and as further discussed below.

Four additional committed programs have been defined, which may combine antibodies from the Servier portfolio with one or more Anticalin proteins based on Pieris’ proprietary platform to generate innovative immuno-oncology bispecific drug candidates (“Collaboration Products”). The Servier Collaboration Agreement may be expanded by up to three additional therapeutic programs. Pieris has the option to co-develop and retain commercial rights in the United States for up to three programs beyond the Lead Product (“Co-Development Collaboration Products”), while Servier will be responsible for development and commercialization of the other programs worldwide (“Servier Worldwide Collaboration Products”). Each party is responsible for an agreed upon percentage of shared costs, as set forth in the budget for the collaboration plan, and further discussed below.

Co-Development Collaboration Products may be jointly developed, according to a collaboration plan, through marketing approval from the U.S. Food and Drug Administration (“FDA”) or European Medicines Agency (“EMA”). Servier Worldwide Collaboration Products may be jointly developed, according to a collaboration plan, through specified preclinical activities, at which point Servier becomes responsible for further development of the collaboration product.

At inception, Servier was granted the following licenses: (i) development license for the Lead Product, (ii) commercial license for the Lead Product, (iii) individual research licenses for each of the four Collaboration Products, and (iv) individual non-exclusive platform technology licenses for each of the Lead Product and four Collaboration Products. Upon achievement of certain development activities, specified by the collaboration for each Servier Collaboration Agreement, Servier will be granted a development license and a commercial license. For the Lead Product and Co-Development Collaboration Products, the licenses granted are with respect to the entire world except for the United States. For Servier Worldwide Collaboration Products, the licenses granted are with respect to the entire world.

The Servier Agreements will be managed on an overall basis by a joint executive committee (“JEC”) formed by an equal number of members from the Company and Servier. Decisions by the JEC will be made by consensus, however, in the event of a disagreement, each party will have final-decision making authority as it relates to the applicable territory in which such party has commercialization rights for the applicable product. In addition to the JEC, the Collaboration Agreement requires the participation of both parties on: (i) a JSC, (ii) a JDC, (iii) a Joint Intellectual Property Committee (“JIPC”), and (iv) a Joint Research Committee (“JRC”). The responsibilities of these committees vary, depending on the stage of development and commercialization of the Lead Product and each of the Collaboration Products.

For the Lead Product and Co-Development Collaboration Products, Pieris and Servier are responsible for an agreed upon percent of the shared costs required to develop the products through commercialization. In the event that Pieris fails to exercise their option to co-develop the Co-Development Collaboration Products, Servier has the right to continue with the development and will be responsible for all costs required to develop the products through commercialization.

Under the Servier Agreements, the Company received an upfront, non-refundable payment of €30.0 million (approximately $32.0 million). In addition, the Company is eligible to receive research, development, commercial, and sales milestone payments as well as tiered royalties up to low double digits on the sales of commercialized products in the Servier territories.

The initial research collaboration term, as it relates to the Lead Product and Collaboration Products, shall continue for three years from the effective date, and may be mutually extended for two one-year terms consecutively applied. The term of the Servier Agreements ends upon the expiration of all Servier’s payment obligations under the respective Servier Agreements.

The term of the individual Servier Agreements end upon the expiration of all of Servier’s payment obligations under such Servier Collaboration Agreement. The Servier Collaboration Agreements may be terminated by Servier for convenience beginning 12 months after their effective date upon 180 days’ notice. The Servier Collaboration Agreements may also be terminated by Servier or Pieris for material breach upon 90 days’ or 120 days’ notice of a material breach, with respect to the Servier Collaboration Agreement and License Agreement, respectively, provided that the applicable party has not cured such breach by the applicable 90-day or 120-day permitted cure period, and dispute resolution procedures specified in the applicable Servier Collaboration Agreement have been followed. The Servier Collaboration Agreements may also be terminated due to the other party’s insolvency or for a safety issue and may in certain instances be terminated on a product-by-product and/or country-by-country basis. The License Agreement will terminate upon termination of the Servier Collaboration Agreement, on a product-by-product and/or country-by-country basis.

The Company accounted for the Servier Agreements as a multiple element arrangement under ASC 605-25. The arrangement with Servier contains the following initial deliverables: (i) five non-exclusive platform technology licenses, (ii) development license for the Lead Product, (iii) commercial license for the Lead Product, (iv) research and development services for the Lead Product, (v) participation on each of the committees, (vi) four research licenses for Collaboration Products, and (vii) research and development services for the Collaboration Products. Additionally, as the development and commercial licenses on the four Collaboration Products may be granted at discount in the future, the Company determined such discounts be included as an element of the arrangement at inception.

Management considered whether any of the deliverables could be considered separate units of accounting. The Company determined the licenses granted, at arrangement inception, did not have standalone value from the research and development services to be provided for the Lead Product and Collaboration Products, over the term of the Servier Agreements, due to the specific nature of the intellectual property and knowledge required to perform the research and development services. The Company determined that the participation on the various committees did have standalone value from the delivered licenses as the services could be performed by an outside party.

As a result, management concluded there are ten units of accounting at inception of the agreement: (i) combined unit of accounting representing a non-exclusive platform technology license, commercial license, development license and research and development services for the Lead Product, (ii) four units of accounting each representing a combined non-exclusive platform technology license, research license, and research and development services for each Collaboration Product (iii) one unit of accounting representing the participation of the various governance committees, and (iv) four units of accounting representing the discounts on the development and commercial licenses granted for the Collaboration Products upon the achievement of specified preclinical activities.

The Company determined that neither VSOE nor TPE is available for any of the units of accounting identified at arrangement inception. Accordingly, the selling price of each unit of accounting was developed using BESP. The Company developed its best estimate of selling price for licenses by applying a risk adjusted, net present value, estimate of future potential cash flows approach, which included the cost of obtaining research and development services at arm’s length from a third-party provider, as well as internal full time equivalent costs to support these services.

The Company developed the BESP for committee participation by using management’s best estimate of the anticipated participation hours multiplied by a market rate for comparable participants.

The Company developed the BESP for the discounts granted on the licenses by probability weighting multiple cash flow scenarios using the income approach.

Allocable arrangement consideration at inception is comprised of the upfront fee of €30.0 million (approximately $32.0 million) and was allocated among the separate units of accounting using the relative selling price method.

The amounts allocated to the combined unit of accounting for the Lead Product and four units of accounting for the four Collaboration Products will be recognized on a proportional performance basis as the activities are conducted over the life of the arrangement. The term of the performance at inception of the agreement for the Lead Product and each of the Co-Developed Collaboration Products may be through approval of certain regulatory bodies; a period which could be many years. The term of the performance at inception of the agreement for each of the other two Servier Worldwide Collaboration Products is approximately two to three years. The amounts allocated to the participation on each of the committees will be recognized ratably over the anticipated performance period over the entirety of the arrangement with Servier. The amounts allocated to the discounts of the development and commercial licenses granted in the future will be recognized upon delivery of each of the licenses assuming no other performance obligations.

Additionally, the Company evaluated payments required to be made between both parties as a result of the shared development costs of the Lead Product and Co-Development Collaboration Products. The Company will classify payments made as a reduction of revenue and will classify payments received as revenue, in the period they are earned.

Under the Servier Agreements the Company is eligible to receive various research, development, commercial, and sales milestones. Management determined certain research, development and commercial milestones, which may be received under the Servier Agreements, are substantive when the Company is involved in the development and commercialization of the applicable product. Payments related to the achievement of such milestones, if any, will be recognized as revenue when the milestone is achieved. Total potential substantive research, development and commercial milestones are up to €163.0 million. Research, development, and commercial milestones are deemed non-substantive if they are based solely on the performance of another party. Non-substantive milestones will be treated as contingent revenue and will be recognized when achieved, to the extent the Company has no remaining performance obligations under the arrangement. Milestone payments earned upon the achievement of sales events will be recognized when earned.

The Company will recognize royalty revenue in the period of sale for the related product(s), based on the underlying contract terms, provided that the reported sales are reliably measurable and the Company has no remaining performance obligations, assuming all other revenue recognition criteria are met.

As of December 31, 2017, there is $ 4.1 million and $30.2 million of deferred revenue and non-current deferred revenue, respectively, related to the Servier Agreements.

F. Hoffmann-La Roche Ltd and Hoffmann- La Roche Inc.

In December 2015, the Company entered into a Research Collaboration and License Agreement (the “Roche Agreement”) with F. Hoffmann- La Roche Ltd. and Hoffmann- La Roche Inc., (“Roche”), for the research, development, and commercialization of Anticalin-based drug candidates against a predefined, undisclosed target in cancer immune therapy. The parties will jointly pursue a preclinical research program, targeting the identification and generation of Anticalin proteins that bind to a specific target, for an expected period of 20 months, which may be extended by Roche for up to an additional 12 months. Roche has the ability to continue exclusivity rights for up to an additional 5 years. Both Roche and the Company will participate in a joint research committee in connection with this agreement. Following the research program, Roche will be responsible for subsequent pre-clinical and clinical development of any product developed through the research plan and will have worldwide commercialization rights to any such product.

Effective September 28, 2017, Roche exercised their option to extend the initial period for the research program until April 30, 2018. Effective November 20, 2017, a second amendment to the Roche Agreement provided Roche the option to extend this period until up to August 31, 2018, which it did on February 26, 2018.

The Company received $6.5 million upfront upon entering the Roche Agreement. Additionally, Roche will pay Pieris for research services provided by Pieris in conjunction with the research program. Roche will also pay Pieris for certain milestones relating to development, regulatory, and sales milestones, as they are achieved. Revenue recognition is associated with the portion of the research services performed during the periods as well as the value of research services provided by Pieris in connection with the ongoing research program. As of December 31, 2017, $1.5 million of deferred revenue remains related to the Roche Agreement.

The Company identified the research and commercial licenses, performance of R&D services, and participation in the joint research committee as deliverables under the Roche Agreement. For revenue recognition purposes, management determined that there are two units of accounting at the inception of the agreement representing (i) the research and commercial licenses and the performance of R&D services which do not have standalone value, and (ii) the participation in the joint research committee. The upfront consideration received was allocated to the units of accounting and is being recognized on a proportional performance basis as the activities are conducted over the life of the Roche Agreement.

Management determined that the development and regulatory milestones are not substantive because they do not relate solely to past performance of the Company and the Company’s involvement in the achievement is limited to progress reports and other updates. Non-substantive milestones will be recognized when achieved to the extent the Company has no remaining performance obligations under the arrangement.

Other Collaborations

The Company has entered into several other research and collaboration agreements for which the Company could achieve future milestone payments. For revenue recognition purposes, management determined these milestones to be substantive in accordance with applicable accounting guidance related to milestone revenue. Substantive uncertainty existed at the inception of the arrangements as to whether the milestones would be achieved because of the numerous variables, such as the high rate of failure inherent in research and development activities and the uncertainty involved with obtaining regulatory approval. No milestones or other revenues related to these agreements were recognized during the year ended December 31, 2017. For the year ended December 31, 2016, the Company recognized a milestone payment under one of these other agreements, which is based on the initiation of a toxicity study in non-human primates.

Cash, Cash Equivalents and Investments

12 Months Ended

Dec. 31, 2017

Cash and Cash Equivalents [Abstract]

Cash, cash equivalents and investments

As of December 31, 2017, cash, cash equivalents and investment comprised funds in depository, money market accounts, U.S. treasury securities, asset backed securities, and corporate bonds. None of these cash equivalents and investments existed as of December 31, 2016. The following table presents the cash equivalents and investments carried at fair value in accordance with the hierarchy defined in Note 2 (in thousands):



	Total		Quoted prices in active markets (Level 1)		Significant other observable inputs (Level 2)		Significant unobservable inputs (Level 3)
December 31, 2017
Money market funds, included in cash equivalents	$	4,583	$	4,583			$	—
Corporate bonds, included in cash equivalents	13,595				13,595		—
Investments - U.S. treasuries	4,172		4,172				—
Investments - Asset-backed securities	6,384				6,384		—
Investments - Corporate bonds	34,117				34,117		—
Total	$	62,851	$	8,755	$	54,096	$	—

Cash equivalents and marketable securities have been initially valued at the transaction price and subsequently valued, at the end of each reporting period, utilizing third party pricing services or other market observable data. The pricing services utilize industry standard valuation models, including both income and market based approaches and observable market inputs to determine value. The Company validates the prices provided by its third-party pricing services by reviewing their pricing methods and obtaining market values from other pricing sources, as needed. After completing its validation procedures, the Company did not adjust any fair value measurements provided by the pricing services as of December 31, 2017.

Cash equivalents and investments at December 31, 2017 consist of the following (in thousands):



	Contractual maturity (in days)	Amortized Cost		Unrealized gains		Unrealized losses			Fair Value
Investments
U.S. treasuries	212-340	$	4,287	$	—	$	(115	)	$	4,172
Asset-backed securities	197-365	2,709		—		(14		)	2,695
Asset-backed securities	greater than 365	3,798		—		(110		)	3,688
Corporate bonds	91-365	28,356		—		(473		)	27,882
Corporate bonds	greater than 365	6,344		1		(108		)	6,236
Total		$	45,494	$	1	$	(820	)	$	44,673

Property and Equipment, Net

12 Months Ended

Dec. 31, 2017

Property, Plant and Equipment [Abstract]

Property and equipment, net

Property and equipment are summarized as follows (in thousands):



	Years Ended December 31,
	2017			2016
Laboratory equipment	$	6,101		$	3,869
Office and computer equipment	494			499
Leasehold improvements	318			321
Property and equipment at cost	6,913			4,689
Accumulated depreciation	(2,879		)	(2,425		)
Property and equipment, net	$	4,034		$	2,264

Depreciation expense was $0.4 million and $0.4 million for the years ended December 31, 2017 and 2016, respectively. There were no other changes in accumulated depreciation other than the foreign currency impact.

Accrued Expenses

12 Months Ended

Dec. 31, 2017

Payables and Accruals [Abstract]

Accrued Expenses

Accrued expenses and other current liabilities consisted of the following (in thousands):



	Years Ended December 31,
	2017		2016
Compensation expense	$	2,325	$	1,198
Professional fees	1,322		624
Research and development fees	791		1,284
Audit and tax fees	424		455
Other current liabilities	1,308		158
Total	$	6,170	$	3,719

Income Taxes

12 Months Ended

Dec. 31, 2017

Income Tax Disclosure [Abstract]

Income Taxes

The Company reported a loss before income taxes consisting of the following (in thousands):



	Years Ended December 31,
	2017			2016
Domestic	$	(13,840	)	$	(8,725	)
Foreign	(2,704		)	(13,913		)
Loss before income taxes	$	(16,544	)	$	(22,637	)

The components of the provision (benefit) for income taxes are as follows (in thousands):



	Years Ended December 31,
	2017		2016
Current:
Federal	$	—	$	—
State	—		—
Foreign	1,103		162
Total current	1,103		162
Deferred:
Federal	—		—
State	—		—
Foreign	—		—
Total deferred	—		—
Provision (benefit) for income taxes	$	1,103	$	162

The reconciliation of the federal statutory rate to Pieris’ effective tax rate is as follows:



	2017		2016
Federal income tax rate	34.0	%	34.0	%
Tax Reform - Change in enacted rate	(22.2	)
Foreign rate differential	(1.2	)	(2.9	)
State tax, net of federal benefit	2.4		0.9
Permanent items	—		(2.3	)
Other	1.8		(0.9	)
Withholding tax	—		(0.7	)
Change in valuation allowance	(21.5	)	(28.8	)
Effective income tax rate	(6.7	)%	(0.7	)%

The components of deferred tax assets and liabilities related to net tax effects of temporary differences between the carrying amount of assets and liabilities for financial reporting purposes and the amounts used for income taxes purposes were as follows (in thousands):



	Years Ended December 31,
	2017			2016
Deferred tax assets:
Net operating loss carryforwards	$	22,170		$	18,498
Share based awards compensation	1,280			1,080
Accrued compensation/other	296			239
Deferred Revenue	1,504			—
Total deferred tax assets	25,250			19,817
Less: valuation allowance:	(25,250		)	(19,817		)
Net deferred tax asset	$	—		$	—

The Company operates in multiple jurisdictions. Accordingly, the Company files United States federal and state income tax returns as well as returns in multiple foreign jurisdictions. In assessing the realizability of deferred tax assets, management considers whether it is more likely than not that some portion or all deferred tax assets will not be realized. The ultimate realization of deferred tax assets is dependent upon the generation of future taxable income during the periods in which those temporary differences become deductible. Management considers the scheduled reversal of deferred tax liabilities, projected future taxable income, and tax-planning strategies in making this assessment. Management believes it is more likely than not that the results of future operations will not generate sufficient taxable income in the U.S. or in its foreign jurisdictions to realize the full benefits of its deferred tax assets. As of December 31, 2017, we continue to maintain a full valuation allowance against all net deferred tax assets.

The increase in the valuation allowance of deferred tax assets of $5.5 million was primarily influenced by the operating losses generated in current tax year, and the impact of deferred revenue.

As of December 31, 2017, the Company had net operating loss carryforwards for United States federal income tax purposes of $24.5 million and net operating loss carryforwards for state income tax purposes of $21.3 million. These tax loss carryforwards expire through 2037. In the United States, utilization of the NOL carryforwards may be subject to a substantial annual limitation under Section 382 of the Internal Revenue Code of 1986 and similar state provisions due to ownership change limitations that have occurred previously or that could occur in the future. These ownership changes may limit the amount of NOL carryforwards that can be utilized annually to offset future taxable income and tax, respectively. The Company has not currently completed a study to assess whether an ownership change has occurred, or whether there have been multiple ownership changes since the Acquisition.

As of December 31, 2017, the Company had German corporate income tax and trade tax net operating loss carryforwards of approximately $46.1 million and $45.6 million respectively. Under current German laws, tax loss carryforwards may only be used to offset any relevant later assessment period (calendar year) $1.2 million plus 60% of the exceeding taxable income and trade profit of such period. In addition, certain transactions, including transfers of shares or interest in the loss holding entity, may result in the partial or total forfeiture of tax losses existing at that date. Partial or total forfeiture of tax losses may further occur in corporate reorganizations of the loss holding entity. Tax years ended December 31, 2013 or later remain subject to examination by the German tax authorities.

The Company accounts for uncertain tax positions pursuant to ASC 740 which prescribes a recognition threshold and measurement process for financial statement recognition of uncertain tax positions taken or expected to be taken in a tax return. If the tax position meets this threshold, the benefit to be recognized is measured at the largest amount of benefit that is more likely than not (determined by cumulative probability) of being realized upon ultimate settlement with the taxing authority. The Company recorded an uncertain tax position related to a prior year position, that if successfully challenged by tax authorities could result in the loss of certain tax attributes. The balance of uncertain tax positions will remain until such time that settlement is reached with the relevant tax authorities or should the statute of limitations expire. The Company recognizes interest and penalties, if any, related to uncertain tax positions in income tax expense. No interest and penalties related to uncertain tax positions were accrued at December 31, 2017 and December 31, 2016.

The following table sets forth a reconciliation of the beginning and ending amounts of unrecognized tax benefits, excluding the impact of interest and penalties, for the years ended December 31, 2017 and 2016 (in thousands):



Unrecognized tax benefits at December 31, 2016	$	5,655
Currency translation adjustment	796
Unrecognized tax benefits at December 31, 2017	$	6,451

Enacted Tax Legislation

The Company does not expect unrecognized tax benefits to change significantly over the next twelve months. The full amount of unrecognized tax benefits would impact the effective rate, subject to valuation allowance considerations, if recognized. On December 22, 2017, the Tax Cuts and Jobs Act of 2017 (the “Act”) was signed into law making significant changes to the Internal Revenue Code. Changes include, but are not limited to, a corporate tax rate decrease from 35% to 21% effective for tax years beginning after December 31, 2017, the transition of U.S international taxation from a worldwide tax system to a territorial system, and a one-time transition tax on the mandatory deemed repatriation of cumulative foreign earnings as of December 31, 2017. ASC 740 requires the tax effects of changes in tax laws must be recognized in the period in which the law is enacted, or December 22, 2017 for the Act. ASC 740 also requires deferred tax assets and liabilities to be measured at the enacted tax rate expected to apply when temporary differences are to be realized or settled. Thus, at the date of enactment, the Company’s deferred taxes were re-measured utilizing the new federal income tax rate of 21%. On December 22, 2017, the SEC staff issued Staff Accounting Bulletin No. 118, Income Tax Accounting Implications of the Tax Cuts and Jobs Act, or SAB 118, which allows the recording of provisional amounts during a measurement period not to extend beyond one year of the enactment date. In accordance with SAB 118, we have determined that our deferred tax asset value and associated valuation allowance reduction of $3.7 million is a provisional amount and a reasonable estimate at December 31, 2017. The final impact may differ from this provisional amount due to, among other things, changes in interpretations and assumptions we have made thus far and the issuance of additional regulatory or other guidance. We expect to complete the final impact within the measurement period. The Company has quantified the impact of the rate reduction from 34% to 21% in its balance sheet. No other aspect of the Act had a material effect on the Company’s consolidated financial statements or related footnote disclosure.

Australian Tax Credits

From time to time, the Company's Australian subsidiary has applied for and received cash tax credit, irrespective of a tax liability, based on certain qualifying activities. The Australian research and development Tax Incentive credit is a self-assessed, entitlement program that provides a credit for eligible research and development entities engaging in qualifying research and development activities. The level of credit is based upon a percentage of the research and development entity’s aggregated turnover for the income tax year, subject to income limitations and provided that the research and development entity is not controlled by an exempt entity or combination of exempt entities. Pieris records the Australian research and development tax credit as an offset to research and development expenses in the consolidated statements of operations, which follows the income statement classification of the original expenses. For the year ended December 31, 2016, the Company recorded $1.5 million as an expense offset, along with a receivable of $1.5 million at December 31, 2016. The Company did not apply for this tax incentive credit in 2017.

Stockholders' Equity	12 Months Ended
Stockholders' Equity	Dec. 31, 2017
Equity [Abstract]
Stockholders' equity	Stockholders’ equity Common Stock During the year ended December 31, 2017, the Company issued 453,209 net shares of common stock upon exercise of stock options. Stock options to purchase 182,471 shares of common stock were net exercised resulting in the net issuance of 83,491 shares of common stock and stock options to purchase 369,718 shares of common stock were exercised for cash, providing cash proceeds of $0.8 million. No stock options were exercised during the 2016 period. During the year ended December 31, 2017, the Company issued 1,505,026 shares of common stock due to warrant exercises. Net exercise of 89,330 shares of common stock underlying the warrants resulted in the issuance of 49,127 shares of common stock. Additionally, 1,455,899 were exercised resulting in cash proceeds of $3.3 million. No warrants were exercised during the 2016 period. Each share of the Company’s common stock is entitled to one vote and all shares rank equally as to voting and other matters. Dividends may be declared and paid on the common stock from funds legally available therefor, if, as and when determined by the Board of Directors. Private Placement and Preferred Stock In June 2016, the Company entered into a securities purchase agreement (the “Securities Purchase Agreement”) for a private placement of the Company’s securities with a select group of institutional investors (the “2016 PIPE”). The 2016 PIPE sale transaction, by the Company, consisted of 8,188,804 units at a price of $2.015 per unit for gross proceeds, to the Company, of approximately $16.5 million. After deducting for placement agent fees and offering expenses, the aggregate net proceeds from the private placement was approximately $15.3 million. Each unit consisted of (i) one share of the Company’s Common Stock or non-voting series A convertible preferred stock (the “Series A Convertible Preferred Stock”) which are convertible into one-thousand shares of common stock, (ii) one warrant to purchase 0.4 shares of Common Stock at an exercise price of $2.00 per share and (iii) one warrant to purchase 0.2 shares of Common Stock at an exercise price of $3.00 per share. The warrants will be exercisable for a period of five years from the date of issuance. Each share of Series A Convertible Preferred Stock was issued at a price of $2.015 per share, and is convertible into 1,000 shares of common stock, provided the holder and/or its affiliates do not own greater than 9.99% of the total number of Pieris common stock then outstanding. The Series A Convertible Preferred Stock has a par value of $0.001 per share, has no registration or voting rights, and holders are entitled to receive dividends on a pari passu basis with the Company´s common stock, when, and if declared. In event of a true liquidation or winding down of the business, holders of Series A Convertible Preferred Stock will be paid prior to the holders of Common Stock. In connection with the 2016 PIPE, the Company issued 3,225,804 shares of Common Stock and 4,963 shares of Series A Convertible Preferred Stock to the 2016 PIPE investors. The Company has 4,963 shares of preferred stock both issued and outstanding during the years ended December 31, 2017 and 2016, respectively.

Net Loss per Share	12 Months Ended
Net Loss per Share	Dec. 31, 2017
Earnings Per Share [Abstract]
Net Loss per Share	Net Loss per Share Basic net loss per share is calculated by dividing net income (loss) by the weighted average shares outstanding during the period, without consideration for common stock equivalents. Diluted net loss per share is calculated by adjusting weighted average shares outstanding for the dilutive effect of common stock equivalents outstanding for the period, determined using the treasury-stock and if-converted methods. For purposes of the diluted net loss per share calculation, preferred stock, stock options, and warrants are considered to be common stock equivalents but have been excluded from the calculation of diluted net loss per share, as their effect would be anti-dilutive for all periods presented. Therefore, basic and diluted net loss per share were the same for all periods presented. For the years ended December 31, 2017 and 2016, and as calculated using the treasury stock method, approximately 14.4 million and 8.2 million of weighted average shares, respectively, were excluded from the calculation of diluted weighted average shares outstanding as their effect was antidilutive.

Stock and Employee Benefit Plans

12 Months Ended

Dec. 31, 2017

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Stock and employee benefit plans

In December 2014, the Company adopted the 2014 Employee, Director and Consultant Equity Incentive Plan, (the “2014 Plan”) which provides for the grant of stock options to certain designated employees of the Company, non-employee directors of the Company and certain other persons performing significant services for the Company as designated by the Compensation Committee of the Board of Directors. The 2014 Plan was terminated on June 28, 2016 when the Company adopted the 2016 Employee, Director and Consultant Equity Incentive Plan, (the “2016 Plan”). Therefore, no options were granted under the 2014 Plan and no options are available for future grant after this date.

The 2016 Plan provides for the grant of stock options, restricted and unrestricted stock awards, and other stock-based awards to employees of the Company, non-employee directors of the Company, and certain other consultants performing services for the Company as designated by either the Board of Directors or the Compensation Committee of the Board of Directors. The 2016 Plan authorizes the issuance of up to 3,750,000 shares of common stock plus awards canceled or expired under the 2014 Plan, if any. Shares which are vested or continue to vest can still be exercised under the 2014 Plan. The 2016 Plan does not provide for an “evergreen” provision. The vesting periods of equity incentives issued under the 2016 Plan are determined by the Compensation Committee of the Company´s Board of Directors, with stock options generally vesting over a four-year period.

The Company’s stock options have a maximum term of 10 years from the date of grant. Stock options granted under the 2014 Plan or 2016 Plan may be either incentive stock options or nonqualified stock options. The exercise price of stock options granted under the 2014 Plan and 2016 Plan must be at least equal to the fair market value of the common stock on the date of grant. The Company’s general policy is to issue common shares upon the exercise of stock options.

The Company estimates the fair value of each employee stock award on the grant date using the Black-Scholes option-pricing model based on the following assumptions:



	Years Ended December 31,
	2017	2016
Risk free interest rate	1.77% - 2.22%	1.13% - 2.08%
Expected term	5.00 - 5.73 years	5.00 - 5.73 years
Dividend yield	—	—
Expected volatility	75.1% - 78.9%	74.9% - 76.0%

The weighted-average fair value of the 1,852,682 and 1,873,047 options granted during the years ended December 31, 2017 and 2016 was $2.47 and $1.00, respectively.

Total stock-based compensation expense is recorded in operating expenses based upon the functional responsibilities of the individuals holding the respective options as follows (in thousands):



	Years Ended December 31,
	2017		2016
Research and development	$	844	$	599
General and administrative	2,202		1,306
Total stock-based compensation	$	3,046	$	1,905

As of December 31, 2017, there were 1,612,514 shares available for future grant under the 2016 Plan, including 194,542 shares which were forfeited under the 2014 Plan.

The following table summarizes stock option activity for employees and nonemployees (shares in thousands):



	Number of Options		Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Life	Aggregate Intrinsic Value (in thousands)
Outstanding, December 31, 2016	4,423		$	1.99		$	—
Granted	1,853		3.23			4
Exercised	(552	)	2.34			886
Canceled	(280	)	2.78			277
Outstanding, December 31, 2017	5,444		$	2.33	8.07 years	$	28,395
Vested or expected to vest, December 31, 2017	5,444		$	2.33	8.07 years	$	28,395
Exercisable, December 31, 2017	3,067		$	1.96	7.32 years	$	17,141

Periodically, the Company grants options outside of the 2014 and 2016 Plans as inducement options, which are material awards to the executive officers or other personnel entering senior leadership roles with the Company. These awards are excluded from the table above. The following table summarizes stock option activity for these inducement options (in thousands):



	Number of Options		Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Life	Aggregate Intrinsic Value (in thousands)
Outstanding, December 31, 2016	1,000		$	2.41		$	—
Granted	625		$	5.24		$	—
Canceled	(94	)	$	1.45		$	572
Outstanding, December 31, 2017	1,531		$	3.62	8.79 years	$	6,015
Vested or expected to vest	1,531		$	3.62	8.79 years	$	6,015
Exercisable, December 31, 2017	688		$	2.23	8.39 years	$	3,657

The compensation expense with all inducement options was $0.8 million of which $0.3 million is included in research and development expense and $0.5 million is included in general and administration expense for the year ended December 31, 2017. The compensation expense for inducement options for the year ended December 31, 2016 was $0.3 million and is included in research and development expense.

As of December 31, 2017, the total unrecognized compensation cost related to non-vested awards was $6.4 million of which $2.4 million are for inducement options. The Company expects to recognize the compensation cost over a remaining weighted-average period of 3.28 years.

401(k) Savings plan

In 2015, the Company established a defined-contribution savings plan under Section 401(k) of the Internal Revenue Code (the “401(k) Plan”). The 401(k) Plan covers all U.S. based employees who meet defined minimum age and service requirements, and allows participants to defer a portion of their annual compensation on a pretax basis. The Company made matching contributions to participants in this plan which totaled $45 thousand and $32 thousand for the years ended December 31, 2017 and 2016, respectively.

License and Transfer Agreement	12 Months Ended
License and Transfer Agreement	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
License and Transfer Agreement	License and Transfer Agreement In April 2016, the Company entered into a license and transfer agreement (the “Original Agreement”) with Enumeral Biomedical Holdings, Inc. (“Enumeral”), pursuant to which the Company acquired a non-exclusive worldwide license to use specified patent rights and know-how owned by Enumeral to research, develop and market fusion proteins. As contemplated by the terms of the Original Agreement, the Company entered into a definitive license and transfer agreement (the “Definitive Agreement”) with Enumeral on June 6, 2016, to expand the scope of the Company’s option to license additional antibodies from Enumeral. Under the Definitive Agreement, Enumeral granted Pieris options to license two additional undisclosed Enumeral antibodies (each, a “Subsequent Option”). The Subsequent Options expired unexercised on May 31, 2017. Under the terms of the Original Agreement, the Company agreed to pay Enumeral an upfront license fee of $250 thousand upon signing in April 2016 and subsequently elected to pay a $750 thousand maintenance fee in May 2016. All amounts paid pursuant to the Original Agreement were recorded as research and development expense in the period they were incurred. No license or maintenance fees were incurred for the year ended December 31, 2017. On January 29, 2018, Enumeral filed a voluntary petition for relief under Chapter 11 of the United States Bankruptcy Code in the Bankruptcy Court for the District of Massachusetts (the “Bankruptcy Court”). Enumeral continues to operate its business as a debtor in possession under the jurisdiction of the Bankruptcy Court. Prior to and in contemplation of its bankruptcy filing, on January 26, 2018, Enumeral entered into an Asset Purchase Agreement (the “Purchase Agreement”) with XOMA US LLC. The Purchase Agreement contemplates that Enumeral will sell specified assets of its PD-1 antibody program, including without limitation, all of its rights under the Definitive License Agreement (collectively, the “PD-1 Assets”). The Bankruptcy Court approved a process pursuant to which Enumeral will solicit higher or better offers for the PD-1 Assets and conduct an auction process to determine the ultimate purchaser. The process contemplates that the winning bidder will purchase the PD-I Assets, including the Definitive License Agreement, with the sale contemplated to close in early April 2018. We will have an opportunity to vet the proposed purchaser to ensure that they (i) can continue to perform Enumeral’s obligations under the Definitive License Agreement, and (ii) will not interfere with our use of the rights we currently enjoy under the Definitive License Agreement.

Commitments and Contingencies

12 Months Ended

Dec. 31, 2017

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies

Licensing Commitments

The Company has license agreements with two parties under which the Company is obliged to pay annual license fees. One agreement requires annual license payments for Strep-tag technology that represents tool technologies used for research purposes only. This agreement expires in 2024. Another license agreement also requires a minimum annual license fee for an exclusive license to certain patents related to the Company's core Anticalin technology platform. This agreement expires upon expiration of the last patent subject to that agreement. The minimum annual license fee commitments under the two agreements as of December 31, 2017 (in thousands):



	License payments
2018	$	96
2019	96
2020	96
2021	96
2022	96
Thereafter	372
Total minimum license payments	$	852

The Company is also obliged to pay low single digit royalties, including annual minimum royalties, on sales of products that utilize its core Anticalin technology platform. Should the Company grant licenses or sublicenses to those patents to third parties, it will be obliged to share a percentage of resulting revenue with the licensee, which percentage of resulting revenue is creditable against annual license payments. In addition, payment obligations are reduced by the Company's proportionate contribution to a joint invention. Payment obligations terminate on expiration or annulment of the last patent covered by the agreement.

Leases

The Company leases office and laboratory space in Freising, Germany as well as office space in Boston, Massachusetts. The German lease agreement has a defined termination date, which is eight months after the end of each quarter, with unlimited renewal periods at the Company's discretion. In June 2016, the Company entered into a second lease agreement for additional office space in the same building, which has a fixed term of one year along with unlimited renewal periods. As Pieris did not cancel this lease agreement by June 2017, the term of the lease extended by one year until June 2019. In August 2015, the Company entered into an Agreement of Sublease to lease approximately 3,950 square feet in Boston, MA. The term of the lease expires in February 2022.

The Company records rent expense on a straight-line basis over the lease term period. For the years ended December 31, 2017 and 2016 respectively, the Company recognized rent expense under its existing lease agreements in an amount of $0.5 million and $0.5 million for the years ended December 31, 2017 and 2016, respectively.

The Company’s contractual commitments of the non-cancellable portion under these operating leases as of December 31, 2017 are as follows (in thousands):



	Total
2018	$	456
2019	218
2020	200
2021	204
2022	34
Total minimum lease payments	$	1,112

Subsequent Events	12 Months Ended
Subsequent Events	Dec. 31, 2017
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events License and Collaboration Agreement and Non-Exclusive Anticalin Platform Technology License Agreement with Seattle Genetics On February 8, 2018, the Company, together with Pieris GmbH, entered into a License and Collaboration Agreement and a Non-Exclusive Anticalin Platform Technology License Agreement (collectively the “Seattle Genetics Agreements”) with Seattle Genetics, pursuant to which the parties will develop multiple targeted bispecific immuno-oncology treatments for solid tumors and blood cancers. Under the terms of the Seattle Genetics Agreements, Seattle Genetics paid Pieris a $30 million upfront fee, tiered royalties on net sales up to the low double-digits, and will pay up to $1.2 billion in total success-based payments across three product candidates. The companies will pursue multiple antibody-Anticalin fusion proteins during a research phase, and Seattle Genetics has the option to select up to three therapeutic programs for further development. Prior to the initiation of a pivotal trial, Pieris may opt into global co-development and U.S. commercialization of the second program and share in global costs and profits on a 50/50 basis. Seattle Genetics will solely develop, fund and commercialize the other two programs. Seattle Genetics may also decide to select additional candidates from the initial research phase for further development in return for the payment to Pieris of additional fees, milestone payments, and royalties. The term of each of the Seattle Genetics Agreements ends upon the expiration of all of Seattle Genetics’ payment obligations under such Agreement. The License and Collaboration Agreement may be terminated by Seattle Genetics in its entirety for convenience beginning 12 months after its effective date upon 90 days notice or, for any program where a pivotal study has been initiated, upon 180 days notice. Any program may be terminated at Seattle Genetics’ option. If any program is terminated by Seattle Genetics after a pre-defined pre-clinical stage, Pieris will have full rights to continue such program. If any program is terminated by Seattle Genetics prior to such pre-defined pre-clinical stage, Pieris will have the right to continue to develop such program, but will be obligated to offer a co-development option to Seattle Genetics for such program. The License and Collaboration Agreement may also be terminated by Seattle Genetics or Pieris for an uncured material breach by the other party upon 90 days notice, subject to extension for an additional 90 days if the material breach relates to diligence obligations and subject, in all cases, to dispute resolution procedures. The License and Collaboration Agreement may also be terminated due to the other party’s insolvency and may in certain instances, including for reasons of safety, be terminated on a product-by-product basis. Each party may also terminate the Seattle Genetics Agreements if the other party challenges the validity of any patents licensed under the Seattle Genetics Agreements, subject to certain exceptions. The Non-Exclusive Anticalin Platform Technology License Agreement will terminate upon termination of the License and Collaboration Agreement, whether in its entirety or on a product-by-product basis. Other License Agreement Updates Our collaboration with Roche On February 26, 2018, pursuant to the Roche Agreement, as amended, Roche provided notice to Pieris of its extension of the research term of the Roche Agreement to continue until August 31, 2018. Our collaboration with Daiichi Sankyo Daiichi Sankyo Company Limited (“Daiichi Sankyo” or "Daiichi") partnered with Pieris to research, develop and commercialize two Anticalin therapeutics pursuant to a May 31, 2011 Collaboration Research and Technology Licensing Agreement (the “DS Collaboration Agreement”). On May 8, 2017, Daiichi Sankyo discontinued the development of one of those two therapeutics, a PSCK9 program (DS-9001), after having advanced this program to first-in-human studies for strategic reasons. Consequentially, this Anticalin program, including respective intellectual property rights, were transferred back to Pieris. The second of these two therapeutic programs pursued under the DS Collaboration Agreement is an Anticalin protein directed to calcitonin gene-related peptide (“CGRP”) for therapeutic use in the treatment of migraine headaches. The CGRP program is in the IND-enabling stage and Pieris previously reported Daiichi Sankyo’s decision to initiate a GLP toxicity study in connection with this program. Due to Daiichi Sankyo’s strategic prioritization and commercial reasons related to competing CGRP inhibitors in advanced stages of development, Daiichi Sankyo provided notice to Pieris on March 1, 2018 of its termination of the CGRP program. Pre-clinical data regarding this CGRP antagonizing Anticalin protein indicate that it has good drug-like properties, including strong target affinity, the ability to neutralize the biological activity of CGRP in vitro, and the ability to inhibit vasodilation, a cause of migraine pain, in rat skin following subcutaneous administration of the antagonist. In connection with the termination of the development of the CGRP program, and under the terms of the DS Collaboration Agreement, Daiichi Sankyo is obligated to carry out certain activities to facilitate transfer of activities, regulatory filings, materials, data, agreements and other matters to Pieris in connection with the return to Pieris of the development program related to the CGRP program. Pieris intends to diligently review the data associated with the program and consider its strategic options thereafter. The foregoing summary of the terms relating to the DS Collaboration Agreement, including with respect to Daiichi Sankyo’s termination of such DS Collaboration Agreement with respect to the CGRP program, is qualified in its entirety by the terms of the DS Collaboration Agreement, which were filed with the SEC as exhibit 10.7 to the Form 10-K filed on March 30, 2017. The contents of such exhibit are hereby incorporated by reference. As a result of the termination of the DS Collaboration Agreement, the Company is no longer eligible for future research, development and regulatory milestones. Underwritten Public Offering In February 2018, the Company completed an underwritten public offering of its common stock in which it sold 6,325,000 shares of Common Stock, including the exercise in full by the underwriters of their option to purchase an additional 825,000 shares of Common Stock, to the public at a price of $8.00 per share. The offering was completed under the shelf registration statement that was filed on Form S-3 and declared effective by the SEC on August 3, 2016. Net proceeds of the underwritten public offering, after deducting the underwriting discounts and commissions, were $47.6 million, excluding offering expenses of approximately $0.3 million incurred by the Company.

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2017

Accounting Policies [Abstract]

Basis of Consolidation

Use of Estimates

Foreign Currency Translation

Cash, Cash Equivalents and Investments

Concentration of Credit Risk and Other Risks and Uncertainties

Concentration of Credit Risk and Off-Balance Sheet Risk

Fair Value Measurement


•	Level 1 inputs are quoted prices in active markets for identical assets or liabilities that the reporting entity has the ability to access at the measurement date.


•	Level 2 utilizes quoted market prices in markets that are not active, broker or dealer quotations, or alternative pricing sources with reasonable levels of price transparency.


•	Level 3 inputs are unobservable inputs for the asset or liability in which there is little, if any, market activity for the asset or liability at the measurement date.

Financial instruments measured at fair value on a recurring basis include cash equivalents and investments (Note 4).

Fair Values of Financial Instruments

Accounts Receivable

Property and Equipment



Asset Classification		Estimated useful life (in years)
Leasehold improvements		shorter of useful life or remaining life of the lease
Laboratory equipment		10 - 14
Office and computer equipment		3 - 13

Impairment of Long-lived Assets

Revenue Recognition

Multiple-Element Arrangements

Milestone Payments and Royalties

Research and Development

Incremental direct cost

Income Taxes

Stock-based Compensation

Contingencies

Segment Reporting

Earnings per Share

Recent Accounting Pronouncements

Standards not yet adopted

Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2017

Accounting Policies [Abstract]

Estimated Useful Life of Property and Equipment

The estimated useful life of the different groups of property and equipment is as follows:



Asset Classification		Estimated useful life (in years)
Leasehold improvements		shorter of useful life or remaining life of the lease
Laboratory equipment		10 - 14
Office and computer equipment		3 - 13

Revenue (Tables)

12 Months Ended

Dec. 31, 2017

Revenue from Contract with Customer [Abstract]

Revenue

During the years ended December 31, 2017 and 2016, respectively, the Company recognized revenues as follows (in thousands):



	Years Ended December 31,
	2017		2016
License fees	$	11,285	$	2,736
Research and development services	1,403		1,440
Milestone payments	12,573		1,655
Other revenues	14		—
Total Revenue	$	25,275	$	5,831

During the years ended December 31, 2017 and 2016, respectively, the Company recognized revenue from the following strategic partnerships and other license agreements (in thousands):



	Years Ended December 31,
	2017		2016
AstraZeneca	$	19,769	$	—
Servier	1,907		—
Roche	3,516		4,080
Other	83		1,751
Total Revenue	$	25,275	$	5,831

Potential Milestone Payments

Under the Company´s existing strategic partnerships and other license agreements, Pieris could receive the following potential milestone payments (in millions):



	Research, Development & Regulatory Milestones		Sales Milestones
AstraZeneca	$	1,111	$	960
Servier	1,040		942
Roche	290		123
Other	68		—
Total potential milestone payments	$	2,509	$	2,025

Cash, Cash Equivalents and Investments (Tables)

12 Months Ended

Dec. 31, 2017

Cash and Cash Equivalents [Abstract]

Cash Equivalents and Investments

The following table presents the cash equivalents and investments carried at fair value in accordance with the hierarchy defined in Note 2 (in thousands):



	Total		Quoted prices in active markets (Level 1)		Significant other observable inputs (Level 2)		Significant unobservable inputs (Level 3)
December 31, 2017
Money market funds, included in cash equivalents	$	4,583	$	4,583			$	—
Corporate bonds, included in cash equivalents	13,595				13,595		—
Investments - U.S. treasuries	4,172		4,172				—
Investments - Asset-backed securities	6,384				6,384		—
Investments - Corporate bonds	34,117				34,117		—
Total	$	62,851	$	8,755	$	54,096	$	—

Cash equivalents and investments at December 31, 2017 consist of the following (in thousands):



	Contractual maturity (in days)	Amortized Cost		Unrealized gains		Unrealized losses			Fair Value
Investments
U.S. treasuries	212-340	$	4,287	$	—	$	(115	)	$	4,172
Asset-backed securities	197-365	2,709		—		(14		)	2,695
Asset-backed securities	greater than 365	3,798		—		(110		)	3,688
Corporate bonds	91-365	28,356		—		(473		)	27,882
Corporate bonds	greater than 365	6,344		1		(108		)	6,236
Total		$	45,494	$	1	$	(820	)	$	44,673

Property and Equipment, Net (Tables)

12 Months Ended

Dec. 31, 2017

Property, Plant and Equipment [Abstract]

Summary of Property and Equipment

Property and equipment are summarized as follows (in thousands):



	Years Ended December 31,
	2017			2016
Laboratory equipment	$	6,101		$	3,869
Office and computer equipment	494			499
Leasehold improvements	318			321
Property and equipment at cost	6,913			4,689
Accumulated depreciation	(2,879		)	(2,425		)
Property and equipment, net	$	4,034		$	2,264

Accrued Expenses (Tables)

12 Months Ended

Dec. 31, 2017

Payables and Accruals [Abstract]

Accrued Expenses and Other Current Liabilities

Accrued expenses and other current liabilities consisted of the following (in thousands):



	Years Ended December 31,
	2017		2016
Compensation expense	$	2,325	$	1,198
Professional fees	1,322		624
Research and development fees	791		1,284
Audit and tax fees	424		455
Other current liabilities	1,308		158
Total	$	6,170	$	3,719

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2017

Income Tax Disclosure [Abstract]

Loss Before Income Taxes

The Company reported a loss before income taxes consisting of the following (in thousands):



	Years Ended December 31,
	2017			2016
Domestic	$	(13,840	)	$	(8,725	)
Foreign	(2,704		)	(13,913		)
Loss before income taxes	$	(16,544	)	$	(22,637	)

Components of the Provision (Benefit) for Income Taxes

The components of the provision (benefit) for income taxes are as follows (in thousands):



	Years Ended December 31,
	2017		2016
Current:
Federal	$	—	$	—
State	—		—
Foreign	1,103		162
Total current	1,103		162
Deferred:
Federal	—		—
State	—		—
Foreign	—		—
Total deferred	—		—
Provision (benefit) for income taxes	$	1,103	$	162

Reconciliation of Federal Statutory Rate to the Effective Tax Rate

The reconciliation of the federal statutory rate to Pieris’ effective tax rate is as follows:



	2017		2016
Federal income tax rate	34.0	%	34.0	%
Tax Reform - Change in enacted rate	(22.2	)
Foreign rate differential	(1.2	)	(2.9	)
State tax, net of federal benefit	2.4		0.9
Permanent items	—		(2.3	)
Other	1.8		(0.9	)
Withholding tax	—		(0.7	)
Change in valuation allowance	(21.5	)	(28.8	)
Effective income tax rate	(6.7	)%	(0.7	)%

Components of Deferred Tax Assets and Liabilities



	Years Ended December 31,
	2017			2016
Deferred tax assets:
Net operating loss carryforwards	$	22,170		$	18,498
Share based awards compensation	1,280			1,080
Accrued compensation/other	296			239
Deferred Revenue	1,504			—
Total deferred tax assets	25,250			19,817
Less: valuation allowance:	(25,250		)	(19,817		)
Net deferred tax asset	$	—		$	—

Schedule of Reconciliation of Unrecognized Tax Benefits Excluding Impact of Interest and Penalties



Unrecognized tax benefits at December 31, 2016	$	5,655
Currency translation adjustment	796
Unrecognized tax benefits at December 31, 2017	$	6,451

Stock and Employee Benefit Plans (Tables)

12 Months Ended

Dec. 31, 2017

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Fair Value Assumptions

The Company estimates the fair value of each employee stock award on the grant date using the Black-Scholes option-pricing model based on the following assumptions:



	Years Ended December 31,
	2017	2016
Risk free interest rate	1.77% - 2.22%	1.13% - 2.08%
Expected term	5.00 - 5.73 years	5.00 - 5.73 years
Dividend yield	—	—
Expected volatility	75.1% - 78.9%	74.9% - 76.0%

Stock Based Compensation Expense

Total stock-based compensation expense is recorded in operating expenses based upon the functional responsibilities of the individuals holding the respective options as follows (in thousands):



	Years Ended December 31,
	2017		2016
Research and development	$	844	$	599
General and administrative	2,202		1,306
Total stock-based compensation	$	3,046	$	1,905

Summary of Stock Option Activity

The following table summarizes stock option activity for employees and nonemployees (shares in thousands):



	Number of Options		Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Life	Aggregate Intrinsic Value (in thousands)
Outstanding, December 31, 2016	4,423		$	1.99		$	—
Granted	1,853		3.23			4
Exercised	(552	)	2.34			886
Canceled	(280	)	2.78			277
Outstanding, December 31, 2017	5,444		$	2.33	8.07 years	$	28,395
Vested or expected to vest, December 31, 2017	5,444		$	2.33	8.07 years	$	28,395
Exercisable, December 31, 2017	3,067		$	1.96	7.32 years	$	17,141



	Number of Options		Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Life	Aggregate Intrinsic Value (in thousands)
Outstanding, December 31, 2016	1,000		$	2.41		$	—
Granted	625		$	5.24		$	—
Canceled	(94	)	$	1.45		$	572
Outstanding, December 31, 2017	1,531		$	3.62	8.79 years	$	6,015
Vested or expected to vest	1,531		$	3.62	8.79 years	$	6,015
Exercisable, December 31, 2017	688		$	2.23	8.39 years	$	3,657

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2017

Commitments and Contingencies Disclosure [Abstract]

Minimum Annual License Fee Commitments

The minimum annual license fee commitments under the two agreements as of December 31, 2017 (in thousands):



	License payments
2018	$	96
2019	96
2020	96
2021	96
2022	96
Thereafter	372
Total minimum license payments	$	852

Contractual Commitments Under Non-Cancellable Portions of Operating Leases

The Company’s contractual commitments of the non-cancellable portion under these operating leases as of December 31, 2017 are as follows (in thousands):



	Total
2018	$	456
2019	218
2020	200
2021	204
2022	34
Total minimum lease payments	$	1,112

Corporate Information (Details) - USD ($) $ in Millions		1 Months Ended
Corporate Information (Details) - USD ($) $ in Millions	Mar. 14, 2018	Feb. 28, 2018	Dec. 31, 2017
Subsequent Event [Line Items]
Cash, cash equivalents and investments			$ 82.6
Subsequent Event
Subsequent Event [Line Items]
Net proceeds from stock offering		$ 47.3
Proceeds from License Fees Received	$ 30.0

Summary of Significant Accounting Policies - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Realized gains (losses) on available-for-sale securities	$ 0	$ 0
Allowance for doubtful accounts	0	$ 0
Impairment of long-lived assets	$ 0

Summary of Significant Accounting Policies - Estimated Useful Life of Property and Equipment (Details)	12 Months Ended
	Dec. 31, 2017
Laboratory equipment \| Minimum
Property, Plant and Equipment [Line Items]
Estimated useful life	10 years
Laboratory equipment \| Maximum
Property, Plant and Equipment [Line Items]
Estimated useful life	14 years
Office and computer equipment \| Minimum
Property, Plant and Equipment [Line Items]
Estimated useful life	3 years
Office and computer equipment \| Maximum
Property, Plant and Equipment [Line Items]
Estimated useful life	13 years

Revenue - Revenue Generated from Non-Product Sales (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Revenue from Contract with Customer [Abstract]
License fees	$ 11,285	$ 2,736
Research and development services	1,403	1,440
Milestone payments	12,573	1,655
Other Revenues	14	0
Total Revenue	$ 25,275	$ 5,831

Revenue - Revenue From Licensing Agreements and Strategic Partnerships (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Disaggregation of Revenue [Line Items]
Revenue	$ 25,275	$ 5,831
AstraZeneca
Disaggregation of Revenue [Line Items]
Revenue	19,769	0
Servier
Disaggregation of Revenue [Line Items]
Revenue	1,907	0
Roche
Disaggregation of Revenue [Line Items]
Revenue	3,516	4,080
Other
Disaggregation of Revenue [Line Items]
Revenue	$ 83	$ 1,751

Revenue - Potential Milestone Payments (Details) - Strategic Partnerships and Other License Agreements - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Research, Development & Regulatory Milestones
Revenue Recognition, Milestone Method [Line Items]
Potential milestone payments	$ 2,509
Sales Milestones
Revenue Recognition, Milestone Method [Line Items]
Potential milestone payments		$ 2,025
AstraZeneca \| Research, Development & Regulatory Milestones
Revenue Recognition, Milestone Method [Line Items]
Potential milestone payments	1,111
AstraZeneca \| Sales Milestones
Revenue Recognition, Milestone Method [Line Items]
Potential milestone payments		960
Servier \| Research, Development & Regulatory Milestones
Revenue Recognition, Milestone Method [Line Items]
Potential milestone payments	1,040
Servier \| Sales Milestones
Revenue Recognition, Milestone Method [Line Items]
Potential milestone payments		942
Roche \| Research, Development & Regulatory Milestones
Revenue Recognition, Milestone Method [Line Items]
Potential milestone payments	290
Roche \| Sales Milestones
Revenue Recognition, Milestone Method [Line Items]
Potential milestone payments		123
Other \| Research, Development & Regulatory Milestones
Revenue Recognition, Milestone Method [Line Items]
Potential milestone payments	$ 68
Other \| Sales Milestones
Revenue Recognition, Milestone Method [Line Items]
Potential milestone payments		$ 0

Revenue - AstraZeneca AB (Details) - USD ($) $ in Thousands		12 Months Ended
Revenue - AstraZeneca AB (Details) - USD ($) $ in Thousands	May 02, 2017	Dec. 31, 2017	Dec. 31, 2016
Deferred Revenue Arrangement [Line Items]
Milestone payments		$ 12,573	$ 1,655
Non-current deferred revenue		46,542	$ 1,409
AstraZeneca
Deferred Revenue Arrangement [Line Items]
Research collaboration agreement term	5 years
Milestone payments		12,600
AstraZeneca \| Upfront Payment
Deferred Revenue Arrangement [Line Items]
Allocable arrangement consideration	$ 45,000
AstraZeneca \| Upfront Payment \| Estimated Development and Manufacturing Services
Deferred Revenue Arrangement [Line Items]
Allocable arrangement consideration	8,200
AstraZeneca \| Upfront Payment \| Relative Selling Price Method
Deferred Revenue Arrangement [Line Items]
Allocable arrangement consideration	$ 53,200
AstraZeneca \| License and Collaboration Agreement
Deferred Revenue Arrangement [Line Items]
Period after effective date agreements may be terminated	12 months
Contract termination advance notice period	90 days
Agreement termination advance notice period if marketing approval obtained	180 days
Agreement termination notice period upon material breach by the Company	180 days
Agreement termination notice period upon breach of payment obligations by the Company	30 days
Contract termination due to material breach, additional notice period if the breach is not susceptible	180 days
AstraZeneca \| Substantive Development and Sales Milestone \| Minimum
Deferred Revenue Arrangement [Line Items]
Milestone payments	$ 72,200
AstraZeneca \| Substantive Development and Sales Milestone \| Maximum
Deferred Revenue Arrangement [Line Items]
Milestone payments	611,400
AstraZeneca \| Non-Substantive Development and Sales Milestones \| Minimum
Deferred Revenue Arrangement [Line Items]
Milestone payments	366,200
AstraZeneca \| Non-Substantive Development and Sales Milestones \| Maximum
Deferred Revenue Arrangement [Line Items]
Milestone payments	1,100,000
AstraZeneca \| Sales Milestones \| Maximum
Deferred Revenue Arrangement [Line Items]
Milestone payments	$ 1,000,000
Deferred revenue		28,600
Non-current deferred revenue		$ 16,300

Revenue - ASKA Pharmaceutical Co. Ltd. (Details) - USD ($) $ in Thousands		12 Months Ended
	Feb. 27, 2017	Dec. 31, 2017	Dec. 31, 2016
Deferred Revenue Arrangement [Line Items]
Milestone payments		$ 12,573	$ 1,655
ASKA Pharmaceutical Co. Ltd.
Deferred Revenue Arrangement [Line Items]
Evaluation period	60 days
Deferred revenue		3,100
ASKA Pharmaceutical Co. Ltd. \| Upfront Payment
Deferred Revenue Arrangement [Line Items]
Upfront option payment	$ 2,750
ASKA Pharmaceutical Co. Ltd. \| Strategic Partnerships and Other License Agreements
Deferred Revenue Arrangement [Line Items]
Agreement termination notice period upon breach of payment obligations by the Company	30 days
Milestone payments		$ 0	$ 0

Revenue - Les Laboratoires Servier and Institut de Recherches Internationales Servier (Details) $ in Thousands, € in Millions			12 Months Ended
	Jan. 04, 2017 EUR (€) extension_option product	Jan. 04, 2017 USD ($) extension_option product	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Deferred Revenue Arrangement [Line Items]
Upfront license payment			$ 11,285	$ 2,736
Milestone payments			12,573	1,655
Non-current deferred revenue			46,542	$ 1,409
Les Laboratoires Servier and Institut de Recherches Internationales Servier \| Minimum
Deferred Revenue Arrangement [Line Items]
Research collaboration agreement term	2 years	2 years
Les Laboratoires Servier and Institut de Recherches Internationales Servier \| Maximum
Deferred Revenue Arrangement [Line Items]
Research collaboration agreement term	3 years	3 years
Les Laboratoires Servier and Institut de Recherches Internationales Servier \| Research and Development Services
Deferred Revenue Arrangement [Line Items]
Research collaboration agreement term	3 years	3 years
Les Laboratoires Servier and Institut de Recherches Internationales Servier \| Research and Development Services \| Extension Term
Deferred Revenue Arrangement [Line Items]
Number of agreement extension options \| extension_option	2	2
Research collaboration agreement term	1 year	1 year
Les Laboratoires Servier and Institut de Recherches Internationales Servier \| Strategic Partnerships and Other License Agreements
Deferred Revenue Arrangement [Line Items]
Number of collaboration products \| product	4	4
Period after effective date agreements may be terminated	12 months	12 months
Contract termination advance notice period	180 days	180 days
Number of worldwide collaboration products \| product	2	2
Les Laboratoires Servier and Institut de Recherches Internationales Servier \| Strategic Partnerships and Other License Agreements \| Minimum
Deferred Revenue Arrangement [Line Items]
Agreement termination notice period upon material breach by the Company	90 days	90 days
Les Laboratoires Servier and Institut de Recherches Internationales Servier \| Strategic Partnerships and Other License Agreements \| Maximum
Deferred Revenue Arrangement [Line Items]
Agreement termination notice period upon material breach by the Company	120 days	120 days
Les Laboratoires Servier and Institut de Recherches Internationales Servier \| Strategic Partnerships and Other License Agreements \| Upfront Payment
Deferred Revenue Arrangement [Line Items]
Upfront license payment	€ 30.0	$ 32,000
Les Laboratoires Servier and Institut de Recherches Internationales Servier \| Substantive Development and Sales Milestone \| Maximum
Deferred Revenue Arrangement [Line Items]
Milestone payments \| €	€ 163.0
Les Laboratoires Servier and Institut de Recherches Internationales Servier \| Sales Milestones \| Maximum
Deferred Revenue Arrangement [Line Items]
Deferred revenue			4,100
Non-current deferred revenue			$ 30,200

Revenue - F. Hoffmann-La Roche Ltd. and Hoffman-La Roche Inc. (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016
Deferred Revenue Arrangement [Line Items]
Upfront license payment		$ 11,285	$ 2,736
Roche
Deferred Revenue Arrangement [Line Items]
Deferred revenue		$ 1,500
Roche \| Upfront Payment
Deferred Revenue Arrangement [Line Items]
Upfront license payment	$ 6,500
Roche \| Research and Development Services
Deferred Revenue Arrangement [Line Items]
Research collaboration agreement term	20 months
Roche \| Research and Development Services \| Extension Term
Deferred Revenue Arrangement [Line Items]
Research collaboration agreement term	5 years

Revenue - Other Collaborations (Details) - USD ($)	12 Months Ended
Revenue - Other Collaborations (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Deferred Revenue Arrangement [Line Items]
Milestone payments	$ 12,573,000	$ 1,655,000
Other \| Strategic Partnerships and Other License Agreements
Deferred Revenue Arrangement [Line Items]
Milestone payments	$ 0

Cash, Cash Equivalents and Investments - Cash Equivalents and Investments Carried at Fair Value (Details) $ in Thousands	Dec. 31, 2017 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds, included in cash equivalents	$ 4,583
Corporate bonds, included in cash equivalents	13,595
Investments - U.S. treasuries	4,172
Investments - Asset-backed securities	6,384
Investments - Corporate bonds	34,117
Total	62,851
Quoted prices in active markets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds, included in cash equivalents	4,583
Corporate bonds, included in cash equivalents
Investments - U.S. treasuries	4,172
Investments - Asset-backed securities
Investments - Corporate bonds
Total	8,755
Significant other observable inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds, included in cash equivalents
Corporate bonds, included in cash equivalents	13,595
Investments - U.S. treasuries
Investments - Asset-backed securities	6,384
Investments - Corporate bonds	34,117
Total	54,096
Significant unobservable inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds, included in cash equivalents	0
Corporate bonds, included in cash equivalents	0
Investments - U.S. treasuries	0
Investments - Asset-backed securities	0
Investments - Corporate bonds	0
Total	$ 0

Cash, Cash Equivalents and Investments - Cash Equivalents and Investments (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	$ 45,494
Unrealized gains	1
Unrealized losses	(820)
Fair Value	44,673
U.S. treasuries
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	4,287
Unrealized gains	0
Unrealized losses	(115)
Fair Value	$ 4,172
U.S. treasuries \| Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contractual maturity	212 days
U.S. treasuries \| Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contractual maturity	340 days
Asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	$ 2,709
Unrealized gains	0
Unrealized losses	(14)
Fair Value	$ 2,695
Asset-backed securities \| Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contractual maturity	197 days
Asset-backed securities \| Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contractual maturity	365 days
Asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	$ 3,798
Unrealized gains	0
Unrealized losses	(110)
Fair Value	$ 3,688
Asset-backed securities \| Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contractual maturity	365 days
Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	$ 28,356
Unrealized gains	0
Unrealized losses	(473)
Fair Value	$ 27,882
Corporate bonds \| Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contractual maturity	91 days
Corporate bonds \| Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contractual maturity	365 days
Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	$ 6,344
Unrealized gains	1
Unrealized losses	(108)
Fair Value	$ 6,236
Corporate bonds \| Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contractual maturity	365 days

Property and Equipment, Net - Summary of Property and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Property and equipment at cost	$ 6,913	$ 4,689
Accumulated depreciation	(2,879)	(2,425)
Property and equipment, net	4,034	2,264
Laboratory equipment
Property, Plant and Equipment [Line Items]
Property and equipment at cost	6,101	3,869
Office and computer equipment
Property, Plant and Equipment [Line Items]
Property and equipment at cost	494	499
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment at cost	$ 318	$ 321

Property and Equipment, Net - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Abstract]
Depreciation expense	$ 369	$ 361

Accrued Expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Accrued expenses
Compensation expense	$ 2,325	$ 1,198
Professional fees	1,322	624
Research and development fees	791	1,284
Audit and tax fees	424	455
Other current liabilities	1,308	158
Total	$ 6,170	$ 3,719

Income Taxes - Loss Before Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Domestic	$ (13,840)	$ (8,725)
Foreign	(2,704)	(13,913)
Loss before income taxes	$ (16,544)	$ (22,637)

Income Taxes - Components of the Provision (Benefit) for Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Current:
Federal	$ 0	$ 0
State	0	0
Foreign	1,103	162
Total current	1,103	162
Deferred:
Federal	0	0
State	0	0
Foreign	0	0
Total deferred	0	0
Provision (benefit) for income taxes	$ 1,103	$ 162

Income Taxes - Reconciliation of Federal Statutory Rate to the Effective Tax Rate (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Federal income tax rate	34.00%	34.00%
Tax Reform - Change in enacted rate	(22.20%)
Foreign rate differential	(1.20%)	(2.90%)
State tax, net of federal benefit	2.40%	0.90%
Permanent items	0.00%	(2.30%)
Other	1.80%	(0.90%)
Withholding tax	0.00%	(0.70%)
Change in valuation allowance	(21.50%)	(28.80%)
Effective income tax rate	(6.70%)	(0.70%)

Income Taxes - Components of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Net operating loss carryforwards	$ 22,170	$ 18,498
Share based awards compensation	1,280	1,080
Accrued compensation/other	296	239
Deferred Revenue	1,504	0
Total deferred tax assets	25,250	19,817
Less: valuation allowance:	(25,250)	(19,817)
Net deferred tax asset	$ 0	$ 0

Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Income Taxes [Line Items]
Increase in the valuation allowance	$ 5,500,000
Uncertain tax positions interest and penalties accrued	0	$ 0
Effect of remeasurement of deferred tax assets and liabilities under Tax Cuts and Jobs Act	3,700,000
Federal
Income Taxes [Line Items]
Net operating loss carryforward	24,500,000
State
Income Taxes [Line Items]
Net operating loss carryforward	21,300,000
Germany \| Corporate Income Tax Carryforwards
Income Taxes [Line Items]
Net operating loss carryforward	46,100,000
Germany \| Trade Tax Carryforwards
Income Taxes [Line Items]
Net operating loss carryforward	$ 45,600,000
Australia
Income Taxes [Line Items]
Australian tax credit from R&D activities		1,500,000
Income taxes receivable		$ 1,500,000

Income Taxes - Reconciliation of Unrecognized Tax Benefits Excluding Impact of Interest and Penalties (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($)
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits, beginning balance	$ 5,655
Currency translation adjustment	796
Unrecognized tax benefits, ending balance	$ 6,451

Stockholders' Equity - Common Stock (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Class of Stock [Line Items]
Cash proceeds from option exercises	$ 781	$ 0
Cash proceeds from exercise of warrants	$ 3,309	$ 0
Common Shares
Class of Stock [Line Items]
Issuance of common stock resulting from exercise of stock options (in shares)	453,209	0
Stock options to purchase shares of common stock (in shares)	182,471
Cash proceeds from option exercises	$ 800
Issuance of common stock resulting from exercise of warrants (in shares)	1,505,026	0
Cash proceeds from exercise of warrants	$ 3,300
Common Shares \| Cashless Exercise
Class of Stock [Line Items]
Issuance of common stock resulting from exercise of stock options (in shares)	83,491
Net exercise of common stock shares underlying warrants (in shares)	89,330
Issuance of shares of common stock from exercise (in shares)	49,127
Common Shares \| Cash-Based Awards
Class of Stock [Line Items]
Issuance of common stock resulting from exercise of stock options (in shares)	369,718
Number of shares called by warrants (in shares)	1,455,899

Stockholders' Equity - Private Placement and Preferred Stock (Details) $ / shares in Units, $ in Millions	1 Months Ended
	Jun. 30, 2016 USD ($) $ / shares shares	Dec. 31, 2017 $ / shares shares	Dec. 31, 2016 $ / shares shares
Class of Stock [Line Items]
Number of shares per unit (in shares)	1
Warrant exercise period	5 years
Par value of preferred stock (in dollars per share) \| $ / shares	$ 0.001	$ 0.001	$ 0.001
Shares of common stock issued (in shares)		45,017,062	43,058,827
Shares of preferred stock issued (in shares)		4,963	4,963
Shares of preferred stock outstanding (in shares)		4,963	4,963
Preferred Stock
Class of Stock [Line Items]
Percentage of beneficial ownership	9.99%
Securities Purchase Agreement
Class of Stock [Line Items]
Number of capital units sold in private placement transaction (in units)	8,188,804
Gross proceeds from private placement units sold \| $	$ 16.5
Net proceeds from private placement units sold \| $	$ 15.3
Issue price per share of preferred stock (in dollars per share) \| $ / shares	$ 2.015
2016 PIPE
Class of Stock [Line Items]
Shares of common stock issued (in shares)	3,225,804
Series A Convertible Preferred Stock
Class of Stock [Line Items]
Price per unit issued (in dollars per share) \| $ / shares	$ 2.015
Number of shares per unit (in shares)	1
Shares issued upon conversion of convertible preferred stock (in shares)	1,000
Series A Convertible Preferred Stock \| Private Placement \| 2016 PIPE
Class of Stock [Line Items]
Shares of preferred stock issued (in shares)	4,963
Tranche A Warrants
Class of Stock [Line Items]
Number of warrants	1
Number of shares to be purchased by a warrant (in shares)	0.4
Exercise price (in dollars per share) \| $ / shares	$ 2.00
Tranche B Warrants
Class of Stock [Line Items]
Number of warrants	1
Number of shares to be purchased by a warrant (in shares)	0.2
Exercise price (in dollars per share) \| $ / shares	$ 3.00

Net Loss per Share (Details) - shares shares in Millions	12 Months Ended
Net Loss per Share (Details) - shares shares in Millions	Dec. 31, 2017	Dec. 31, 2016
Earnings Per Share [Abstract]
Anti-dilutive shares excluded from calculation of weighted average shares outstanding (in shares)	14.4	8.2

Stock and Employee Benefit Plans - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands		12 Months Ended		18 Months Ended
	Jun. 28, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Stock-based compensation expense		$ 3,046	$ 1,905
Unrecognized compensation costs related to nonvested awards		$ 6,400		$ 6,400
Weighted-average compensation cost recognition period		3 years 3 months 11 days
Matching contributions made to employee benefit plans		$ 45	32
Research and development
Defined Benefit Plan Disclosure [Line Items]
Stock-based compensation expense		844	599
General and administrative
Defined Benefit Plan Disclosure [Line Items]
Stock-based compensation expense		$ 2,202	$ 1,306
2014 Stock Plan
Defined Benefit Plan Disclosure [Line Items]
Number of options granted (in shares)				0
Shares available for future grant (in shares)	0
Shares forfeited (in shares)		194,542
2016 Stock Plan
Defined Benefit Plan Disclosure [Line Items]
Number of options granted (in shares)		1,852,682	1,873,047
Shares available for future grant (in shares)		1,612,514		1,612,514
Shares of common stock authorized for issuance (in shares)	3,750,000
Vesting period	4 years
Maximum term of stock options		10 years
Weighted-average fair value (in dollars per share)		$ 2.47	$ 1.00
Executive Officers and Senior Leadership
Defined Benefit Plan Disclosure [Line Items]
Number of options granted (in shares)		625,000
Stock-based compensation expense		$ 800
Unrecognized compensation costs related to nonvested awards		2,400		$ 2,400
Executive Officers and Senior Leadership \| Research and development
Defined Benefit Plan Disclosure [Line Items]
Stock-based compensation expense		300	$ 300
Executive Officers and Senior Leadership \| General and administrative
Defined Benefit Plan Disclosure [Line Items]
Stock-based compensation expense		$ 500

Stock and Employee Benefit Plans - Fair Value Assumptions (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk free interest rate, minimum	1.77%	1.13%
Risk free interest rate, maximum	2.22%	2.08%
Dividend yield	0.00%	0.00%
Expected volatility, minimum	75.10%	74.90%
Expected volatility, maximum	78.90%	76.00%
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term	5 years	5 years
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term	5 years 8 months 23 days	5 years 8 months 23 days

Stock and Employee Benefit Plans - Stock Based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	$ 3,046	$ 1,905
Research and development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	844	599
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	$ 2,202	$ 1,306

Stock and Employee Benefit Plans - Summary of Stock Option Activity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017
2014 and 2016 Stock Plans
Number of Options
Outstanding (in shares)	4,423
Granted (in shares)	1,853
Exercised (in shares)	(552)
Canceled (in shares)	(280)
Outstanding (in shares)	5,444
Vested or expected to vest (in shares)	5,444
Exercisable (in shares)	3,067
Weighted- Average Exercise Price
Outstanding (in dollars per share)	$ 1.99
Granted (in dollars per share)	3.23
Exercised (in dollars per share)	2.34
Cancelled (in dollars per share)	2.78
Outstanding (in dollars per share)	2.33
Vested or expected to vest (in dollars per share)	2.33
Exercisable (in dollars per share)	$ 1.96
Weighted- Average Remaining Contractual Life
Outstanding	8 years 26 days
Vested or expected to vest	8 years 26 days
Exercisable	7 years 3 months 26 days
Aggregate Intrinsic Value
Outstanding	$ 0
Granted	4
Exercised	886
Canceled	277
Outstanding	28,395
Vested or expected to vest	28,395
Exercisable	$ 17,141
Executive Officers and Senior Leadership
Number of Options
Outstanding (in shares)	1,000
Granted (in shares)	625
Canceled (in shares)	(94)
Outstanding (in shares)	1,531
Vested or expected to vest (in shares)	1,531
Exercisable (in shares)	688
Weighted- Average Exercise Price
Outstanding (in dollars per share)	$ 2.41
Granted (in dollars per share)	5.24
Cancelled (in dollars per share)	1.45
Outstanding (in dollars per share)	3.62
Vested or expected to vest (in dollars per share)	3.62
Exercisable (in dollars per share)	$ 2.23
Weighted- Average Remaining Contractual Life
Outstanding	8 years 9 months 15 days
Vested or expected to vest	8 years 9 months 15 days
Exercisable	8 years 4 months 21 days
Aggregate Intrinsic Value
Outstanding	$ 0
Granted	0
Canceled	572
Outstanding	6,015
Vested or expected to vest	6,015
Exercisable	$ 3,657

License and Transfer Agreement (Details) - Enumeral Biomedical Holdings - License and Transfer Agreement - USD ($)	Dec. 31, 2017	May 31, 2016	Apr. 30, 2016
Contingencies And Commitments [Line Items]
Upfront license fee payment	$ 0		$ 250,000
Maintenance fee payment	$ 0	$ 750,000

Commitments and Contingencies - Additional Information (Details) $ in Millions	1 Months Ended		12 Months Ended
	Jun. 30, 2016	Aug. 31, 2015 ft²	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Loss Contingencies [Line Items]
Area of leased property \| ft²		3,950
Rent expenses recognized \| $			$ 0.5	$ 0.5
Freising, Germany
Loss Contingencies [Line Items]
Lease term	1 year
Lease extension term	1 year

Commitments and Contingencies - Minimum Annual License Fee Commitments (Details) - License Agreements $ in Thousands	Dec. 31, 2017 USD ($)
License payments
2018	$ 96
2019	96
2020	96
2021	96
2022	96
Thereafter	372
Total minimum license payments	$ 852

Commitments and Contingencies - Contractual Commitments Under Non-Cancellable Portions of Operating Leases (Details) $ in Thousands	Dec. 31, 2017 USD ($)
Non-Cancellable Commitments Under Operating Leases
2018	$ 456
2019	218
2020	200
2021	204
2022	34
Total minimum lease payments	$ 1,112

Subsequent Events - License and Collaboration Agreement and Non-Exclusive Anticalin Platform Technology License Agreement with Seattle Genetics (Details) - USD ($) $ in Thousands		12 Months Ended
	Feb. 08, 2018	Dec. 31, 2017	Dec. 31, 2016
Subsequent Event [Line Items]
Milestone payments		$ 12,573	$ 1,655
Seattle Genetics \| Subsequent Event
Subsequent Event [Line Items]
Contract termination due to material breach, additional notice period	90 days
Seattle Genetics \| License and Collaboration Agreement \| Subsequent Event
Subsequent Event [Line Items]
Period after effective date agreements may be terminated	12 months
Contract termination advance notice period	90 days
Agreement termination advance notice period if pivotal study has been initiated	180 days
Agreement termination notice period upon material breach by the Company	90 days
Seattle Genetics \| License and Collaboration Agreement \| Maximum \| Subsequent Event
Subsequent Event [Line Items]
Milestone payments	$ 1,200,000
Seattle Genetics \| Upfront Payment \| Subsequent Event
Subsequent Event [Line Items]
Allocable arrangement consideration	$ 30,000

Subsequent Events - Underwritten Public Offering (Details) - Subsequent Event $ / shares in Units, $ in Millions	1 Months Ended
	Feb. 28, 2018 USD ($) $ / shares shares
Subsidiary, Sale of Stock [Line Items]
Price per share sold (in dollars per share) \| $ / shares	$ 8.00
Stock offering costs \| $	$ 0.3
Public Stock Offering
Subsidiary, Sale of Stock [Line Items]
Shares sold in offering (in shares) \| shares	6,325,000
Net proceeds from stock offering \| $	$ 47.6
Over-Allotment Option
Subsidiary, Sale of Stock [Line Items]
Shares sold in offering (in shares) \| shares	825,000