Summary of Significant Accounting Policies | 2. Summary of Significant Accounting Policies Basis of Presentation The accompanying interim condensed financial statements are unaudited. These unaudited interim financial statements have been prepared in accordance with U.S. GAAP (“GAAP”) and following the requirements of the United States Securities and Exchange Commission (“SEC”) for interim reporting. As permitted under those rules, certain footnotes or other financial information that are normally required by GAAP can be condensed or omitted. In management’s opinion, the unaudited interim condensed financial statements have been prepared on the same basis as the audited financial statements and include normal recurring adjustments necessary for the fair presentation of the Company’s financial position and its results of operations and comprehensive loss and its cash flows for the periods presented. These statements do not include all disclosures required by GAAP and should be read in conjunction with the Company’s financial statements and accompanying notes for the fiscal year ended December 31, 2016, which is contained in the Company’s Annual Report on Form 10-K Use of Estimates The condensed financial statements have been prepared in accordance with GAAP, which requires management to make estimates and assumptions that affect the amounts and disclosures reported in the condensed financial statements and accompanying notes. Management bases its estimates on historical experience and on assumptions believed to be reasonable under the circumstances. The estimation process often may yield a range of potentially reasonable estimates of actual future outcomes, and management must select an amount that falls within that range of reasonable estimates. Actual results could differ materially from those estimates. The Company believes significant judgment is involved in estimating revenue, stock-based compensation, accrued clinical expenses, warrant liabilities, and equity instrument valuations. Fair Value of Financial Instruments The Company’s financial instruments during the periods reported consist of cash and cash equivalents, marketable securities, prepaid expenses, other current assets, other assets, accounts payable, accrued interest payable, accrued liabilities, the facility loan, and warrant liabilities. Fair value estimates of these instruments are made at a specific point in time, based on relevant market information. These estimates may be subjective in nature and involve uncertainties and matters of significant judgment. The carrying amounts of financial instruments such as cash and cash equivalents, prepaid expenses, other current assets, other assets, accounts payable, accrued liabilities, and accrued interest payable approximate the related fair values due to the short maturities of these instruments. Based on prevailing borrowing rates available to the Company for loans with similar terms, the Company believes the fair value of the facility loan, considering level 2 inputs, approximates its carrying value. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants at the measurement date. Assets and liabilities that are measured at fair value are reported using a three-level fair value hierarchy that prioritizes the inputs used to measure fair value. This hierarchy maximizes the use of observable and unobservable inputs and is as follows: Level 1—Quoted prices in active markets for identical assets or liabilities that the Company has the ability to access at the measurement date. Level 2—Inputs other than quoted prices in active markets that are observable for the asset or liability, either directly or indirectly. Level 3—Inputs that are significant to the fair value measurement and are unobservable (i.e. supported by little market activity), which requires the reporting entity to develop its own valuation techniques and assumptions. The following tables present the fair value of the Company’s financial assets and liabilities measured at fair value on a recurring basis using the above input categories (in thousands): As of September 30, 2017 Description Level 1 Level 2 Level 3 Fair Value Cash equivalents: Money market funds $ 18,554 $ — $ — $ 18,554 Commercial paper — 2,994 — 2,994 Total cash equivalents 18,554 2,994 — 21,548 Marketable securities: Commercial paper — 44,750 — 44,750 Corporate debt securities — 22,359 — 22,359 Asset-backed securities — 8,071 — 8,071 U.S. treasury securities — 3,980 — 3,980 Total short-term investments — 79,160 — 79,160 Total assets measured at fair value $ 18,554 $ 82,154 $ — $ 100,708 Warrant liability $ — $ — $ 5,862 $ 5,862 Total liabilities measured at fair value $ — $ — $ 5,862 $ 5,862 As of December 31, 2016 Description Level 1 Level 2 Level 3 Fair Value Cash equivalents: Money market funds $ 9,456 $ — $ — $ 9,456 Commercial paper — 599 — 599 Corporate debt securities — 500 — 500 Total cash equivalents 9,456 1,099 — 10,555 Marketable securities: Commercial paper — 4,295 — 4,295 Corporate debt securities — 2,204 — 2,204 Total short-term investments — 6,499 — 6,499 Total assets measured at fair value $ 9,456 $ 7,598 $ — $ 17,054 Warrant liability $ — $ — $ 1,145 $ 1,145 Total liabilities measured at fair value $ — $ — $ 1,145 $ 1,145 The Company estimates the fair value of its corporate debt, asset backed securities, and U.S. treasury securities by taking into consideration valuations obtained from third-party pricing services. The pricing services utilize industry standard valuation models, including both income and market-based approaches, for which all significant inputs are observable, either directly or indirectly, to estimate fair value. These inputs include reported trades of and broker/dealer quotes on the same or similar securities, issuer credit spreads, benchmark securities, prepayment/default projections based on historical data, and other observable inputs. There were no transfers between Level 1 and Level 2 during the periods presented. The Company holds a Level 3 liability associated with common stock warrants that were issued in connection with the Company’s financings completed in September and October 2013, January 2014, and August 2015. The warrants are accounted for as liabilities. During the quarter, the Company changed its valuation technique and began to value its warrant liability using a Black-Scholes option pricing model, the inputs for which include: exercise price of the warrants, market price of the underlying common shares, dividend yield, expected term, volatility, and a risk-free interest rate. Changes to any of these inputs can have a significant impact on the estimated fair value of the warrants. Historically, the Company used a binomial option pricing model to value its warrant liabilities. The inputs for the binomial model are similar to the Black-Scholes model but also incorporate other more complex inputs which, in the Company’s case, have previously included the expected timing, probability and valuation impact of certain potential strategic events. Management concluded that no potential strategic events were expected to occur that could significantly impact the warrant liabilities valuation prior to their expiration (beginning in late 2018 and ending in early 2019). The following table sets forth an activity summary which includes the changes in the fair value of the Company’s Level 3 financial instruments (in thousands): For the Nine Months Ended September 2017 2016 Balance, beginning of period $ 1,145 $ 1,220 Issuance of financial instrument — — Change in fair value 4,996 (43 ) Settlement of financial instrument (279 ) — Balance, end of period $ 5,862 $ 1,177 Cash Equivalents and Marketable Securities The Company considers all highly liquid investments with a maturity at the date of purchase of 90 days or less to be cash equivalents. Cash and cash equivalents consist of deposits with commercial banks in checking, interest-bearing, demand money market accounts, and corporate debt securities. The Company invests excess cash in marketable securities with high credit ratings, which are classified in Level 2 of the fair value hierarchy. These securities consist primarily of corporate debt, commercial paper, asset-backed securities, and U.S. treasury securities and are classified as “available-for-sale.” Realized gains and losses from the sale of marketable securities, if any, are calculated using the specific identification method. Realized gains and losses and declines in value judged to be other-than-temporary are included in interest income or expense in the statements of operations and comprehensive loss. Unrealized holding gains and losses are reported in accumulated other comprehensive loss, in the balance sheets. To date, the Company has not recorded any impairment charges on its marketable securities related to other-than-temporary declines in market value. In determining whether a decline in market value is other-than-temporary, various factors are considered, including the cause, duration of time and severity of the impairment, any adverse changes in the investees’ financial condition, and the Company’s intent and ability to hold the security for a period of time sufficient to allow for an anticipated recovery in market value. The following tables summarize amortized cost, unrealized gain and loss, and fair value (in thousands): Gross Gross Amortized Unrealized Unrealized Estimated Cost Gains Losses Fair Value As of September 30, 2017: Commercial paper 44,750 — — 44,750 Corporate debt securities 22,369 — (10 ) 22,359 Asset-backed securities 8,074 — (3 ) 8,071 U.S. treasury securities 3,980 — — 3,980 $ 79,173 $ — $ (13 ) $ 79,160 Gross Gross Amortized Unrealized Unrealized Estimated Cost Gains Losses Fair Value As of December 31, 2016: Commercial paper 4,295 — — 4,295 Corporate debt securities 2,205 — (1 ) 2,204 $ 6,500 $ — $ (1 ) $ 6,499 Concentration of Credit Risk Cash equivalents and marketable securities consist of financial instruments that potentially subject the Company to a concentration of credit risk to the extent of the fair value recorded in the balance sheets. The Company invests cash that is not required for immediate operating needs primarily in highly liquid instruments that bear minimal risk. The Company has established guidelines relating to the quality, diversification, and maturities of securities to enable the Company to manage its credit risk. The Company is exposed to credit risk in the event of a default by the financial institutions holding its cash, cash equivalents and marketable securities and issuers of investments to the extent recorded on the balance sheets. Certain materials and key components that the Company utilizes in its operations are obtained through single suppliers. Since the suppliers of key components and materials must be named in a new drug application (NDA) filed with the U.S. Food and Drug Administration (FDA) for a product, significant delays can occur if the qualification of a new supplier is required. If delivery of material from the Company’s suppliers were interrupted for any reason, the Company may be unable to supply any of its product candidates for clinical trials. Revenue Recognition The Company recognizes revenue when (i) persuasive evidence of an arrangement exists, (ii) delivery has occurred or services have been rendered, (iii) the price is fixed or determinable, and (iv) collectability is reasonably assured. Payments received in advance of work performed are recorded as deferred revenue and recognized when earned. Collaboration and license agreements may include non-refundable If the Company determines that multiple deliverables in an arrangement exist, the consideration is allocated to one or more units of accounting based upon the relative-selling-price of each element in an arrangement. The relative-selling-price used for each deliverable is based on vendor-specific objective evidence, if available, third-party evidence if vendor-specific objective evidence is not available, or estimated selling price if neither vendor-specific or third-party evidence is available. The Company identifies deliverables at the inception of the arrangement. Each deliverable is accounted for as a separate unit of accounting if both of the following criteria are met: (1) the delivered item or items have value to the customer on a standalone basis and (2) for an arrangement that includes a general right of return relative to the delivered items, delivery or performance of the undelivered items is considered probable and substantially in the Company’s control. Non-refundable The Company recognizes payments that are contingent upon achievement of a substantive milestone in their entirety in the period in which the milestone is achieved. Milestones are defined as events that can only be achieved based on the Company’s performance and there is substantive uncertainty about whether the event will be achieved at the inception of the arrangement. Events that are contingent only on the passage of time or only on counterparty performance are not considered milestones subject to this guidance. Further, the amounts received must relate solely to prior performance, be reasonable relative to all of the deliverables and payment terms within the agreement and commensurate with the Company’s performance to achieve the milestone after commencement of the agreement. Any contingent payment that becomes payable upon achievement of events that are not considered substantive milestones are allocated to the units of accounting previously identified at the inception of an arrangement when the contingent payment is received and revenue is recognized based on the revenue recognition criteria for each unit of accounting. Common Stock Warrant Liability The Company’s outstanding common stock warrants issued in connection with certain equity and debt financings that occurred in 2013 through 2015 are classified as liabilities in the accompanying condensed balance sheets because of certain contractual terms that preclude equity classification. The warrants are recorded at fair value using a Black-Scholes option-pricing model. The warrants are re-measured Stock-Based Compensation Employee and director stock-based compensation is measured at fair value on the grant date of the award. Compensation cost is recognized as expense on a straight-line basis over the vesting period for options and on an accelerated basis for stock options with performance conditions. For stock options with performance conditions, the Company evaluates the probability of achieving performance conditions at each reporting date. The Company begins to recognize the expense when it is deemed probable that the performance conditions will be met. The Company uses the Black-Scholes option pricing model to determine the fair value of stock option awards. The determination of fair value for stock-based awards using an option-pricing model requires management to make certain assumptions regarding subjective input variables such as expected term, dividends, volatility and risk-free interest rate. The Company is also required to make estimates as to the probability of achieving the specific performance criteria. If actual results are not consistent with the Company’s assumptions and judgments used in making these estimates, the Company may be required to increase or decrease compensation expense, which could be material to the Company’s results of operations. Equity awards granted to non-employees Net Loss Per Common Share Basic net loss per share of common stock is based on the weighted average number of shares of common stock outstanding during the period. Diluted net loss per share of common stock is calculated as the weighted average number of shares of common stock outstanding adjusted to include the assumed exercises of stock options and common stock warrants, if dilutive. The calculation of diluted loss per share also requires that, to the extent the average market price of the underlying shares for the reporting period exceeds the exercise price of the common stock warrants and the presumed exercise of such securities are dilutive to net loss per share for the period, adjustments to net loss used in the calculation are required to remove the change in fair value of the common stock warrant liability for the period. Likewise, adjustments to the denominator are required to reflect the related dilutive shares. In all periods presented, the Company’s outstanding stock options, incentive awards and warrants were excluded from the calculation of diluted net loss per share because their effects were antidilutive. The Company’s computation of basic and diluted net loss per share is as follows (in thousands, except share and per share amounts): Three Months Ended Nine Months Ended September 30, September 30, 2017 2016 2017 2016 Numerator: Net loss allocated to common stock-basic $ (8,234 ) $ (5,879 ) $ (22,514 ) $ (19,719 ) Adjustments for revaluation of warrants — — — — Net loss allocated to common stock-diluted $ (8,234 ) $ (5,879 ) $ (22,514 ) $ (19,719 ) Denominator: Weighted average number of common stock shares outstanding—basic 40,035,690 23,447,003 31,848,536 23,447,003 Weighted average number of common stock shares outstanding—diluted 40,035,690 23,447,003 31,848,536 23,447,003 Net loss per share—basic: $ (0.21 ) $ (0.25 ) $ (0.71 ) $ (0.84 ) Net loss per share—diluted: $ (0.21 ) $ (0.25 ) $ (0.71 ) $ (0.84 ) The following table shows the total outstanding common stock equivalents considered anti-dilutive and therefore excluded from the computation of diluted net loss per share (in thousands). Three Months Ended Nine Months Ended September 30, September 30, 2017 2016 2017 2016 Warrants for common stock 1,604 1,667 1,604 1,667 Common stock options 3,788 2,422 3,788 2,422 Performace-based stock options 305 327 305 327 Incentive awards 226 241 226 241 5,923 4,657 5,923 4,657 Recent Accounting Pronouncements Accounting Standards Update 2014-09 In May 2014, the FASB issued Accounting Standards Update 2014-09, Revenue from Contracts with Customers and related amendments 2014-09: No. 2016-08, No. 2016-10, No. 2016-12, The new revenue standard permits two methods of adoption: retrospectively to each prior reporting period presented (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 plans to adopt the new revenue standard in the first quarter of 2018 using the modified retrospective method. While the Company has not completed an assessment of the impact of adoption, the adoption of this guidance may have a material effect on the Company’s financial statements. At the end of 2016, the Company entered into a license agreement. Before executing this agreement, the Company had no revenues for the last two years. The consideration that the Company is eligible to receive under this agreement includes an upfront payment, milestone payments, and royalties. This license agreement is unique and will need to be assessed separately under the five-step process under the new standard. The Company is currently analyzing this agreement to determine the differences in the accounting treatment under the new revenue standard compared to that of the current accounting treatment. The new revenue standard differs from the current accounting standard in many respects, such as in the accounting for variable consideration, including milestone payments and royalties. The Company expects that its evaluation of the accounting for this agreement under the new revenue standard could identify material changes from that of the current accounting treatment and it will also impact its condensed financial statement disclosures. Additionally, the Company will continue to monitor industry activities and any additional guidance provided by regulators, standards setters, or the accounting profession and adjust its assessment and implementation plans accordingly. Accounting Standards Update 2016-02 In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842). Accounting Standards Update 2016-09 In March 2016, the FASB issued ASU No. 2016-09, Improvements to Employee Share-Based Payment Accounting 2016-09). 2016-09 paid-in Accounting Standards Update 2017-09 In May 2017, FASB issued ASU No. 2017-09, Compensation-Stock Compensation (Topic 718)- Scope of Modification Accounting 2017-09 Accounting Standards Update 2017-11 In July 2017, the FASB issued ASU No. 2017-11, Earnings Per Share Distinguishing Liabilities from Equity Derivatives and Hedging 2017-11): Non-controlling |