Summary of Significant Accounting Policies	12 Months Ended
Dec. 31, 2016
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation and Consolidation The consolidated financial statements of the Company include the Company’s accounts and have been prepared in conformity with accounting principles generally accepted in the United States of America (“US GAAP”). During 2015, the Company established a wholly-owned foreign subsidiary in Australia. The consolidated financial statements include the Company’s accounts and those of its wholly-owned subsidiary. All intercompany accounts and transactions and balances have been eliminated during consolidation. The functional currency of the Company and its subsidiaries is the United States (“US”) Dollar. All intercompany accounts, transactions and balances have been eliminated during consolidation. Use of Estimates The preparation of consolidated financial statements in conformity with US GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclosure of contingent assets and liabilities and the reported amounts of revenues and expenses in the consolidated financial statements and the accompanying notes. On an ongoing basis, management evaluates its estimates, including those related to revenue recognition, clinical trial accruals, fair value of redeemable convertible preferred stock call option liability, redeemable convertible preferred stock, income taxes and stock-based compensation. Management bases its estimates on historical experience and on various other market-specific and relevant assumptions that management believes to be reasonable under the circumstances. Actual results could differ from those estimates. Segments The Company operates and manages its business as one reportable and operating segment, which is the business of developing and commercializing therapeutics. The Company’s chief executive officer, who is the chief operating decision maker, reviews financial information on an aggregate basis for purposes of allocating and evaluating financial performance. All revenues have been earned in the United States of America, and all long-lived assets are maintained in the United States of America. Cash and cash equivalents Cash and cash equivalents consist of cash and other highly liquid investments with original maturities of three months or less from the date of purchase. At December 31, 2016 and 2015, the Company’s cash and cash equivalents were comprised of funds held in checking accounts and interest bearing money market accounts. Restricted Cash Restricted cash at December 31, 2016 and 2015, comprises cash balances primarily held as security in connection with the Company’s facility lease agreement and are included in other long term assets on the consolidated balance sheets. Short-term and Long-term Investments All investments have been classified as “available-for-sale” and are carried at fair value as determined based upon quoted market prices or pricing models for similar securities at period end. Generally, those investments with contractual maturities greater than 12 months are considered long-term investments. Unrealized gains and losses, deemed temporary in nature, are reported as a component of accumulated other comprehensive income (loss), net of tax. A decline in the fair value of any security below cost that is deemed other than temporary results in a charge to earnings and the corresponding establishment of a new cost basis for the security. The amortized cost of securities is adjusted for amortization of premiums and accretion of discounts to maturity. Dividend and interest income are recognized when earned. Realized gains and losses are included in earnings and are derived using the specific identification method for determining the cost of securities sold. Fair Value Measurements Fair value accounting is applied for all financial assets and liabilities, including short-term and long-term investments, and non-financial assets and liabilities that are recognized or disclosed at fair value in the consolidated financial statements on a recurring basis (at least annually). The carrying amount of the Company’s financial instruments, including note receivable, accounts payable and accrued expenses and other current liabilities approximate fair value due to their short-term maturities. The redeemable convertible preferred stock call option liability was carried at fair value until the Series B issuance in April 2015. At that time, the redeemable convertible preferred stock call option liability was reclassified to permanent equity with no further fair value measurement required. Concentration of Credit Risk Financial instruments that potentially subject the Company to a concentration of credit risk consist of cash and cash equivalents and investments. All of the Company’s cash and cash equivalents are held at financial institutions that management believes are of high credit quality. Such deposits may, at times, exceed federally insured limits. The Company invests in a variety of financial instruments, such as, but not limited to, corporate debt and United States Treasury and Government agency securities, and by policy, limits the amount of credit exposure with any one financial institution or commercial issuer. The Company has not experienced any material credit losses on its investments. Risk and Uncertainties The Company’s future results of operations involve a number of risks and uncertainties. Factors that could affect the Company’s future operating results and cause actual results to vary materially from expectations include, but are not limited to, uncertainty of results of clinical trials and reaching milestones, uncertainty of regulatory approval of the Company’s potential drug candidates, uncertainty of market acceptance of any of the Company’s product candidates that receive regulatory approval, competition from substitute products and larger companies, securing and protecting proprietary technology, strategic relationships and dependence on key individuals and sole source suppliers. Products developed by the Company require approvals from the U.S. Food and Drug Administration (“FDA”) or other international regulatory agencies prior to commercial sales. There can be no assurance that any of the Company’s product candidates will receive the necessary approvals. If the Company is denied approval, approval is delayed or the Company is unable to maintain approvals, it could have a materially adverse impact on the Company. The Company expects to incur substantial operating losses for the next several years and will need to obtain additional financing in order to complete clinical trials and launch and commercialize any product candidates for which it receives regulatory approval. There can be no assurance that such financing will be available or will be on terms acceptable by the Company. Property and Equipment Property and equipment are stated at cost and depreciated using the straight-line method over the estimated useful lives of the assets, ranging from two to five years. Leasehold improvements are amortized over the shorter of their estimated useful lives or the related lease term. Upon retirement or sale, the cost and related accumulated depreciation are removed from the consolidated balance sheet and the resulting gain or loss is reflected in the consolidated statement of operations and comprehensive income (loss). Impairment of Long-Lived Assets The Company reviews long-lived assets, including property and equipment, for impairment whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. An impairment charge would be recorded when estimated undiscounted future cash flows expected to result from the use of the asset and its eventual disposition are less than its carrying amount. Impairment, if any, is assessed using discounted cash flows or other appropriate measures of fair value. Through December 31, 2016, there have been no such impairment charges. Deferred Offering Costs Deferred offering costs, consisting of legal, accounting and other fees and costs relating to the IPO and follow-on public offering were capitalized. The deferred offering costs were offset against the proceeds received upon the closing of the IPO. There was $2.5 million of deferred offering costs capitalized during 2015 and upon the completion of the IPO, these deferred offering costs were offset against the $58.2 million of proceeds received, net of underwriting discounts and commissions. There was $0.5 million of deferred offering costs capitalized during 2016 and upon the completion of the follow-on public offering, were offset against the $61.6 million of proceeds received, net of underwriting discounts and commissions. As of December 31, 2016 and 2015, there were no deferred offering costs capitalized in other long term assets on the consolidated balance sheets. Redeemable Convertible Preferred Stock The Company recorded all shares of redeemable convertible preferred stock at their respective fair values on the dates of issuance. In the event of a change of control of the Company, proceeds were to be distributed in accordance with the liquidation preferences set forth in the amended and restated certificate of incorporation unless the holders of redeemable convertible preferred stock have converted their redeemable convertible preferred shares into common shares. Therefore, the redeemable convertible preferred stock was classified outside of stockholders’ deficit on the accompanying consolidated balance sheets as events triggering the liquidation preferences are not solely within the Company’s control. The carrying value of each series of redeemable convertible preferred stock was being accreted to its respective redemption value through the Company’s IPO in October 2015 upon which it was converted to common stock. Redeemable Convertible Preferred Stock Call Option The Company determined that the Company’s obligation to issue additional shares of the Company’s redeemable convertible preferred stock represented a freestanding financial instrument. The freestanding redeemable convertible preferred stock call option liability was initially recorded at fair value, with fair value changes recognized as increases or reductions in the consolidated statements of operations and comprehensive income (loss). The Company adjusted the liability for changes in fair value until the Series B issuance in April 2015. At that time, the redeemable convertible preferred stock call option liability was reclassified to permanent equity with no further fair value measurement required. The Company had recorded a redeemable convertible preferred stock call option liability, net in September 2012 related to the Series A redeemable convertible preferred stock financing, which was extinguished in July 2014 at the time of the final closing of the Series A redeemable convertible preferred stock. Additionally, the Company had recorded a redeemable convertible preferred stock call option liability in August 2014 related to the Collaboration Agreement, from which the call option expired in April 2015 at the time of the closing of the Company’s Series B redeemable convertible preferred stock financing. Revenue Recognition The Company generates revenue from collaboration and license agreements for the development and commercialization of its products. Collaboration and license agreements may include non-refundable upfront license fees, partial or complete reimbursement of research and development costs, contingent consideration payments based on the achievement of defined collaboration objectives and royalties on sales of commercialized products. To date, the Company has not recognized revenue from sales of its product candidates. The Company recognizes revenue when all four of the following criteria have been met: (i) collectability is reasonably assured; (ii) delivery has occurred or services have been rendered; (iii) persuasive evidence of an arrangement exists; and (iv) the fee is fixed or determinable. Revenue under collaboration and license arrangements is recognized based on performance requirements of the contract. Collectability is assessed based on evaluation of payment criteria as stated in the contract as well as the creditworthiness of the collaboration partner. Determination of whether delivery has occurred or services rendered are based on management’s evaluation of the performance obligations as stated in the contract and progress made against those obligations. Evidence of arrangement is deemed to exist upon execution of the contract. Fees are considered fixed and determinable when the amount payable to the Company is no longer subject to any acceptance, refund rights or other contingencies that would alter the fixed nature of the fees charged for the deliverables. License and collaboration agreements may contain multiple elements as evaluated under Accounting Standards Codification (ASC) 605-25, Revenue Recognition- Multiple-Element Arrangements, including agreements to provide research and development services, and manufacturing and commercialization services, grants of licenses to intellectual property rights and know-how, as well as participation in development and/or commercialization committees. Each deliverable under the agreement is evaluated to determine whether it qualifies as a separate unit of accounting based on whether the deliverable has standalone value to the customer. The arrangement’s consideration that is fixed or determinable is then allocated to each separate unit of accounting based on the following hierarchy: (i) vendor-specific objective evidence of the fair value of the deliverable, if it exists; (ii) third-party evidence of selling price, if vendor-specific objective evidence is not available; or (iii) the best estimate of selling price if neither vendor-specific objective evidence or third-party evidence is available. Upfront payments for licenses are evaluated to determine if the licensee can obtain standalone value from the license separate from the value of the research and development services and other deliverables in the arrangement to be provided by the Company. The assessment of multiple-element arrangements also requires judgment in order to determine the allocation of revenue to each deliverable and the appropriate period of time over which the revenue should be recognized. If the Company determines that the license does not have standalone value separate from the research and development services, the license and the services are combined as one unit of accounting and upfront payments are recorded initially as deferred revenue in the consolidated balance sheet. Revenue is then recognized on a straight-line basis over an estimated performance period that is consistent with the term of performance obligations, unless the Company determines there is a discernible pattern of performance other than straight-line, in which case the Company uses a proportionate performance method to recognize the revenue over the estimated performance period. If the license is determined to have standalone value, then the allocated consideration is recorded as revenue when the license is delivered. License and collaboration agreements may also contain milestone payments that become due upon the achievement of certain milestones. The Company applies ASC 605-28, Revenue Recognition—Milestone Method. Under the milestone method, payments that are contingent upon achievement of a substantive milestone are recognized in the period in which the milestone is achieved. Substantive milestones are defined as an event 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, for the milestone to be considered substantive, 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. Research and Development Expenses Research and development costs are expensed as incurred and consist of salaries and benefits, lab supplies and facility costs, as well as fees paid to others that conduct certain research and development activities on the Company’s behalf. Amounts incurred in connection with collaboration and license agreements are also included in research and development expense. Preclinical Study and Clinical Trial Accruals The Company’s preclinical study and clinical trial accruals are a component of research and development expenses and based on patient enrollment and related costs at clinical investigator sites as well as estimates for the services received and efforts expended pursuant to contracts with multiple research institutions and clinical research organizations (“CROs”) that conduct and manage clinical trials on the Company’s behalf. The Company estimates preclinical study and clinical trial expenses based on the services performed, pursuant to contracts with research institutions and CROs that conduct and manage preclinical studies and clinical trials on its behalf. The Company estimates these expenses based on discussions with internal clinical management personnel and external service providers as to the progress or stage of completion of trials or services and the contracted fees to be paid for such services. If the actual timing of the performance of services or the level of effort varies from the original estimates, the Company will adjust the accrual accordingly. Payments made to third parties under these arrangements in advance of the performance of the related services by the third parties are recorded as prepaid expenses until the services are rendered. Stock-Based Compensation The Company accounts for stock-based compensation arrangements with employees in accordance with ASC 718, Stock Compensation. Stock-based awards granted include stock options with time-based vesting, performance-based stock options and market-based stock options. ASC 718 requires the recognition of compensation expense, using a fair value-based method, for costs related to all stock-based payments. The Company’s determination of the fair value of stock options with time-based vesting on the date of grant utilizes the Black-Scholes option-pricing model, and is impacted by its common stock price as well as other variables including, but not limited to, expected term that options will remain outstanding, expected common stock price volatility over the term of the option awards, risk-free interest rates and expected dividends. Stock-based compensation expense for performance stock options is based on the probability of achieving certain performance criteria, as defined in the individual option grant agreement. The Company estimates the number of performance options ultimately expected to vest and recognizes stock-based compensation expense for those options expected to vest when it becomes probable that the performance criteria will be met and the options vest. The Company has also granted stock options to purchase common stock that vest upon the achievement of market-based stock price targets. The fair value of a stock-based award is recognized over the period during which an optionee is required to provide services in exchange for the option award, known as the requisite service period (usually the vesting period) on a straight-line basis. Stock-based compensation expense recognized at fair value includes the impact of estimated forfeitures. The Company estimates future forfeitures at the date of grant and revises the estimates, if necessary, in subsequent periods if actual forfeitures differ from those estimates. Equity instruments issued to non-employees are recorded at their fair value on the measurement date and are subject to periodic adjustments as the underlying equity instruments vest. The fair value of options granted to consultants is expensed when vested. Non-employee stock-based compensation expense was not material for all periods presented. Estimating the fair value of equity-settled awards as of the grant date using valuation models, such as the Black-Scholes option pricing model, is affected by assumptions regarding a number of complex variables. Changes in the assumptions can materially affect the fair value and ultimately how much stock-based compensation expense is recognized. These inputs are subjective and generally require significant analysis and judgment to develop. Income Taxes The Company provides for income taxes under the asset and liability method. Current income tax expense or benefit represents the amount of income taxes expected to be payable or refundable for the current year. Deferred income tax assets and liabilities are determined based on differences between the financial statement reporting and tax bases of assets and liabilities and net operating loss and credit carryforwards, and are measured using the enacted tax rates and laws that will be in effect when such items are expected to reverse. Deferred income tax assets are reduced, as necessary, by a valuation allowance when management determines it is more likely than not that some or all of the tax benefits will not be realized. The Company accounts for uncertain tax positions in accordance with ASC 740-10, Accounting for Uncertainty in Income Taxes. The Company assesses all material positions taken in any income tax return, including all significant uncertain positions, in all tax years that are still subject to assessment or challenge by relevant taxing authorities. Assessing an uncertain tax position begins with the initial determination of the position’s sustainability and is measured at the largest amount of benefit that is greater than fifty percent likely of being realized upon ultimate settlement. As of each balance sheet date, unresolved uncertain tax positions must be reassessed, and the Company will determine whether (i) the factors underlying the sustainability assertion have changed and (ii) the amount of the recognized tax benefit is still appropriate. The recognition and measurement of tax benefits requires significant judgment. Judgments concerning the recognition and measurement of a tax benefit might change as new information becomes available. The Company includes penalties and interest expense related to income taxes as a component of interest and other income, net. Comprehensive Loss Comprehensive loss is defined as a change in equity of a business enterprise during a period, resulting from transactions from non-owner sources. The Company had unrealized income from its available-for-sale securities during the year ended December 31, 2016, which qualified as other comprehensive income and, therefore, have been reflected in the consolidated statement of operations and comprehensive income (loss). Net Loss per Share of Common Stock Basic net loss per common share is calculated by dividing the net loss attributable to common stockholders by the weighted average number of common shares outstanding during the period, without consideration of potentially dilutive securities. Diluted net loss per share is computed by dividing the net loss attributable to common stockholders by the weighted average number of common shares and potentially dilutive securities outstanding for the period. For purposes of the diluted net loss per share calculation, the redeemable convertible preferred stock, common stock subject to repurchase, and stock options are considered to be potentially dilutive securities. Basic and diluted net loss attributable to common stockholders per share is presented in conformity with the two-class method required for participating securities as the convertible preferred stock is considered a participating security. The Company’s participating securities do not have a contractual obligation to share in the Company’s losses. As such, the net loss was attributed entirely to common stockholders. Because the Company has reported a net loss for all periods presented, diluted net loss per common share is the same as basic net loss per common share for those periods. Recent Accounting Pronouncements From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board, or FASB, or other standard setting bodies and adopted by the Company as of the specified effective date. Unless otherwise discussed, the impact of recently issued standards that are not yet effective will not have a material impact on the Company’s consolidated financial statements upon adoption. Under the Jumpstart Our Business Startups Act of 2012, as amended (the “JOBS Act”), the Company meets the definition of an emerging growth company, and has irrevocably elected to opt out of the extended transition period for complying with new or revised accounting standards pursuant to Section 107(b) of the JOBS Act. In November 2016, the FASB issued Accounting Standard Update (“ASU”) No. 2016-18 (Topic 230), Restricted Cash, Statement of Cash Flows. This ASU 2016-18 requires that a statement of cash flows explain the change during the period in the total of cash, cash equivalents, and amounts generally described as restricted cash or restricted cash equivalents. Therefore, amounts generally described as restricted cash and restricted cash equivalents should be included with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on the statement of cash flows. ASU 2016-18 is effective for public business entities for fiscal years beginning after December 15, 2017, and interim periods within those fiscal years, with early adoption permitted. The amendments in this ASU should be applied using a retrospective transition method to each period presented. The adoption of this standard is not expected to have a material impact on the Company’s consolidated financial statements. In August 2016, the FASB issued ASU No. 2016-15 (Topic 230), Statement of Cash Flows– Classification of Certain Cash Receipts and Cash Payments. This ASU addresses the diversity in practice in how certain cash receipts and cash payments are presented and classified in the statement of cash flows under Topic 230, Statement of Cash Flows, and other Topics. This ASU addresses eight specific cash flow issues and provides specific guidance with the objective of reducing the current and potential future diversity in practice. The amendments in this ASU are effective for public business entities for fiscal years beginning after December 15, 2017, and interim periods within those fiscal years. Early adoption is permitted, including adoption in an interim period. The Company has not determined the potential effects of this standard on its consolidated financial statements. In March 2016, the FASB issued ASU 2016-09 (Topic 718), Compensation - Stock Compensation, which simplifies the accounting for employee share-based transactions. The amendments in this update cover such areas as the recognition of excess tax benefits and deficiencies, the classification of those excess tax benefits on the statement of cash flows, an accounting policy election for forfeitures, the amount an employer can withhold to cover income taxes and still qualify for equity classification, and the classification of those taxes paid on the statement of cash flows. ASU 2016-09 is effective for fiscal years, and interim periods within those years, beginning after December 15, 2016. The Company will adopt ASU 2016-09 in the first quarter of 2017. The Company is expecting the adoption of the ASU to have an immaterial impact on the financial statement due to the valuation allowances against deferred tax assets. In February 2016, the FASB issued ASU No. 2016-02 (Topic 842), Leases. This ASU requires an entity to recognize assets and liabilities arising from a lease for both financing and operating leases. The ASU will also require new qualitative and quantitative disclosures to help investors and other financial statement users better understand the amount, timing, and uncertainty of cash flows arising from leases. ASU 2016-02 is effective for fiscal years beginning after December 15, 2018, with early adoption permitted. The Company has not determined the potential effects of this ASU on its consolidated financial statements. In June 2014, the FASB issued ASU 2014-12, Accounting for Share-Based Payments When the Terms of an Award Provide That a Performance Target Could Be Achieved after the Requisite Service Period. This ASU requires that a performance target that affects vesting and could be achieved after the requisite service period be treated as a performance condition. ASU 2014-12 is effective for the Company in its first quarter of 2016. The adoption of ASU 2014-12 did not have a material impact on the Company’s consolidated financial statements and disclosures. In May 2014, the FASB issued ASU No. 2014-09 (Topic 606), Revenue from Contracts with Customers, which supersedes the revenue recognition requirements in ASC 605, Revenue Recognition. This ASU is based on the principle that revenue is recognized to depict the transfer of goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. The ASU also requires additional disclosure about the nature, amount, timing and uncertainty of revenue and cash flows arising from customer contracts, including significant judgments and changes in judgments and assets recognized from costs incurred to obtain or fulfill a contract. In March, April, and May 2016, the FASB issued amended guidance including clarifying guidance on principal versus agent considerations, identification of performance obligations, collectability and noncash considerations. ASU 2014-09 and its amendments are effective for public entities for annual and interim periods beginning after December 15, 2017, with early adoption for fiscal 2017 permitted. The Company plans to adopt the new revenue standards in the first quarter of 2018. Since its formation, the Company has only had transactions which are recognized in revenue which relate to its Collaboration Agreement with Sanofi S.A. The Company is evaluating whether or not the identification of performance obligations and determination of their stand-alone values would remain unchanged under the new revenue standards. The Company is still assessing the impact of the adoption of the new revenue standards on its consolidated financial statements. As the Company completes its evaluation of this new standard, new information may arise that could change the Company’s current understanding of the impact to revenue recognition. Additionally, the Company will continue to monitor industry activities and any additional guidance provided by regulators, standards setters, or the accounting profession and adjust the Company’s assessment and implementation plans accordingly. Reverse Stock Split In October 2015, the Company’s board of directors and stockholders approved an amendment to the Company’s certificate of incorporation to effect a reverse split of shares of the Company’s issued and outstanding common stock at a 1-for-3.675 ratio and a proportional adjustment to the conversion ratio of its redeemable convertible preferred stock. The reverse stock split was effected on October 23, 2015. The par value and the authorized shares of the Company’s common stock and the par value and the authorized, issued and outstanding shares of the Company’s redeemable convertible preferred stock were not adjusted as a result of the reverse stock split. All issued and outstanding shares of common stock and common stock per share amounts and an adjustment to the redeemable convertible preferred stock ratio contained in these consolidated financial statements have been retroactively adjusted to reflect this reverse stock split for all periods presented.

2. Summary of Significant Accounting Policies

Basis of Presentation and Consolidation

The consolidated financial statements of the Company include the Company’s accounts and have been prepared in conformity with accounting principles generally accepted in the United States of America (“US GAAP”). During 2015, the Company established a wholly-owned foreign subsidiary in Australia. The consolidated financial statements include the Company’s accounts and those of its wholly-owned subsidiary. All intercompany accounts and transactions and balances have been eliminated during consolidation.

The functional currency of the Company and its subsidiaries is the United States (“US”) Dollar. All intercompany accounts, transactions and balances have been eliminated during consolidation.

Use of Estimates

The preparation of consolidated financial statements in conformity with US GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclosure of contingent assets and liabilities and the reported amounts of revenues and expenses in the consolidated financial statements and the accompanying notes. On an ongoing basis, management evaluates its estimates, including those related to revenue recognition, clinical trial accruals, fair value of redeemable convertible preferred stock call option liability, redeemable convertible preferred stock, income taxes and stock-based compensation. Management bases its estimates on historical experience and on various other market-specific and relevant assumptions that management believes to be reasonable under the circumstances. Actual results could differ from those estimates.

Segments

The Company operates and manages its business as one reportable and operating segment, which is the business of developing and commercializing therapeutics. The Company’s chief executive officer, who is the chief operating decision maker, reviews financial information on an aggregate basis for purposes of allocating and evaluating financial performance. All revenues have been earned in the United States of America, and all long-lived assets are maintained in the United States of America.

Cash and cash equivalents

Cash and cash equivalents consist of cash and other highly liquid investments with original maturities of three months or less from the date of purchase. At December 31, 2016 and 2015, the Company’s cash and cash equivalents were comprised of funds held in checking accounts and interest bearing money market accounts.

Restricted Cash

Restricted cash at December 31, 2016 and 2015, comprises cash balances primarily held as security in connection with the Company’s facility lease agreement and are included in other long term assets on the consolidated balance sheets.

Short-term and Long-term Investments

All investments have been classified as “available-for-sale” and are carried at fair value as determined based upon quoted market prices or pricing models for similar securities at period end. Generally, those investments with contractual maturities greater than 12 months are considered long-term investments. Unrealized gains and losses, deemed temporary in nature, are reported as a component of accumulated other comprehensive income (loss), net of tax.

A decline in the fair value of any security below cost that is deemed other than temporary results in a charge to earnings and the corresponding establishment of a new cost basis for the security. The amortized cost of securities is adjusted for amortization of premiums and accretion of discounts to maturity. Dividend and interest income are recognized when earned. Realized gains and losses are included in earnings and are derived using the specific identification method for determining the cost of securities sold.

Fair Value Measurements

Fair value accounting is applied for all financial assets and liabilities, including short-term and long-term investments, and non-financial assets and liabilities that are recognized or disclosed at fair value in the consolidated financial statements on a recurring basis (at least annually). The carrying amount of the Company’s financial instruments, including note receivable, accounts payable and accrued expenses and other current liabilities approximate fair value due to their short-term maturities. The redeemable convertible preferred stock call option liability was carried at fair value until the Series B issuance in April 2015. At that time, the redeemable convertible preferred stock call option liability was reclassified to permanent equity with no further fair value measurement required.

Concentration of Credit Risk

Financial instruments that potentially subject the Company to a concentration of credit risk consist of cash and cash equivalents and investments. All of the Company’s cash and cash equivalents are held at financial institutions that management believes are of high credit quality. Such deposits may, at times, exceed federally insured limits. The Company invests in a variety of financial instruments, such as, but not limited to, corporate debt and United States Treasury and Government agency securities, and by policy, limits the amount of credit exposure with any one financial institution or commercial issuer. The Company has not experienced any material credit losses on its investments.

Risk and Uncertainties

The Company’s future results of operations involve a number of risks and uncertainties. Factors that could affect the Company’s future operating results and cause actual results to vary materially from expectations include, but are not limited to, uncertainty of results of clinical trials and reaching milestones, uncertainty of regulatory approval of the Company’s potential drug candidates, uncertainty of market acceptance of any of the Company’s product candidates that receive regulatory approval, competition from substitute products and larger companies, securing and protecting proprietary technology, strategic relationships and dependence on key individuals and sole source suppliers.

Products developed by the Company require approvals from the U.S. Food and Drug Administration (“FDA”) or other international regulatory agencies prior to commercial sales. There can be no assurance that any of the Company’s product candidates will receive the necessary approvals. If the Company is denied approval, approval is delayed or the Company is unable to maintain approvals, it could have a materially adverse impact on the Company.

The Company expects to incur substantial operating losses for the next several years and will need to obtain additional financing in order to complete clinical trials and launch and commercialize any product candidates for which it receives regulatory approval. There can be no assurance that such financing will be available or will be on terms acceptable by the Company.

Property and Equipment

Property and equipment are stated at cost and depreciated using the straight-line method over the estimated useful lives of the assets, ranging from two to five years. Leasehold improvements are amortized over the shorter of their estimated useful lives or the related lease term. Upon retirement or sale, the cost and related accumulated depreciation are removed from the consolidated balance sheet and the resulting gain or loss is reflected in the consolidated statement of operations and comprehensive income (loss).

Impairment of Long-Lived Assets

The Company reviews long-lived assets, including property and equipment, for impairment whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. An impairment charge would be recorded when estimated undiscounted future cash flows expected to result from the use of the asset and its eventual disposition are less than its carrying amount. Impairment, if any, is assessed using discounted cash flows or other appropriate measures of fair value. Through December 31, 2016, there have been no such impairment charges.

Deferred Offering Costs

Deferred offering costs, consisting of legal, accounting and other fees and costs relating to the IPO and follow-on public offering were capitalized. The deferred offering costs were offset against the proceeds received upon the closing of the IPO. There was $2.5 million of deferred offering costs capitalized during 2015 and upon the completion of the IPO, these deferred offering costs were offset against the $58.2 million of proceeds received, net of underwriting discounts and commissions. There was $0.5 million of deferred offering costs capitalized during 2016 and upon the completion of the follow-on public offering, were offset against the $61.6 million of proceeds received, net of underwriting discounts and commissions. As of December 31, 2016 and 2015, there were no deferred offering costs capitalized in other long term assets on the consolidated balance sheets.

Redeemable Convertible Preferred Stock

The Company recorded all shares of redeemable convertible preferred stock at their respective fair values on the dates of issuance. In the event of a change of control of the Company, proceeds were to be distributed in accordance with the liquidation preferences set forth in the amended and restated certificate of incorporation unless the holders of redeemable convertible preferred stock have converted their redeemable convertible preferred shares into common shares. Therefore, the redeemable convertible preferred stock was classified outside of stockholders’ deficit on the accompanying consolidated balance sheets as events triggering the liquidation preferences are not solely within the Company’s control. The carrying value of each series of redeemable convertible preferred stock was being accreted to its respective redemption value through the Company’s IPO in October 2015 upon which it was converted to common stock.

Redeemable Convertible Preferred Stock Call Option

The Company determined that the Company’s obligation to issue additional shares of the Company’s redeemable convertible preferred stock represented a freestanding financial instrument. The freestanding redeemable convertible preferred stock call option liability was initially recorded at fair value, with fair value changes recognized as increases or reductions in the consolidated statements of operations and comprehensive income (loss). The Company adjusted the liability for changes in fair value until the Series B issuance in April 2015. At that time, the redeemable convertible preferred stock call option liability was reclassified to permanent equity with no further fair value measurement required. The Company had recorded a redeemable convertible preferred stock call option liability, net in September 2012 related to the Series A redeemable convertible preferred stock financing, which was extinguished in July 2014 at the time of the final closing of the Series A redeemable convertible preferred stock. Additionally, the Company had recorded a redeemable convertible preferred stock call option liability in August 2014 related to the Collaboration Agreement, from which the call option expired in April 2015 at the time of the closing of the Company’s Series B redeemable convertible preferred stock financing.

Revenue Recognition

The Company generates revenue from collaboration and license agreements for the development and commercialization of its products. Collaboration and license agreements may include non-refundable upfront license fees, partial or complete reimbursement of research and development costs, contingent consideration payments based on the achievement of defined collaboration objectives and royalties on sales of commercialized products. To date, the Company has not recognized revenue from sales of its product candidates.

The Company recognizes revenue when all four of the following criteria have been met: (i) collectability is reasonably assured; (ii) delivery has occurred or services have been rendered; (iii) persuasive evidence of an arrangement exists; and (iv) the fee is fixed or determinable. Revenue under collaboration and license arrangements is recognized based on performance requirements of the contract. Collectability is assessed based on evaluation of payment criteria as stated in the contract as well as the creditworthiness of the collaboration partner. Determination of whether delivery has occurred or services rendered are based on management’s evaluation of the performance obligations as stated in the contract and progress made against those obligations. Evidence of arrangement is deemed to exist upon execution of the contract. Fees are considered fixed and determinable when the amount payable to the Company is no longer subject to any acceptance, refund rights or other contingencies that would alter the fixed nature of the fees charged for the deliverables.

License and collaboration agreements may contain multiple elements as evaluated under Accounting Standards Codification (ASC) 605-25, Revenue Recognition- Multiple-Element Arrangements, including agreements to provide research and development services, and manufacturing and commercialization services, grants of licenses to intellectual property rights and know-how, as well as participation in development and/or commercialization committees. Each deliverable under the agreement is evaluated to determine whether it qualifies as a separate unit of accounting based on whether the deliverable has standalone value to the customer. The arrangement’s consideration that is fixed or determinable is then allocated to each separate unit of accounting based on the following hierarchy: (i) vendor-specific objective evidence of the fair value of the deliverable, if it exists; (ii) third-party evidence of selling price, if vendor-specific objective evidence is not available; or (iii) the best estimate of selling price if neither vendor-specific objective evidence or third-party evidence is available.

Upfront payments for licenses are evaluated to determine if the licensee can obtain standalone value from the license separate from the value of the research and development services and other deliverables in the arrangement to be provided by the Company. The assessment of multiple-element arrangements also requires judgment in order to determine the allocation of revenue to each deliverable and the appropriate period of time over which the revenue should be recognized. If the Company determines that the license does not have standalone value separate from the research and development services, the license and the services are combined as one unit of accounting and upfront payments are recorded initially as deferred revenue in the consolidated balance sheet. Revenue is then recognized on a straight-line basis over an estimated performance period that is consistent with the term of performance obligations, unless the Company determines there is a discernible pattern of performance other than straight-line, in which case the Company uses a proportionate performance method to recognize the revenue over the estimated performance period. If the license is determined to have standalone value, then the allocated consideration is recorded as revenue when the license is delivered.

License and collaboration agreements may also contain milestone payments that become due upon the achievement of certain milestones. The Company applies ASC 605-28, Revenue Recognition—Milestone Method. Under the milestone method, payments that are contingent upon achievement of a substantive milestone are recognized in the period in which the milestone is achieved. Substantive milestones are defined as an event 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, for the milestone to be considered substantive, 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.

Research and Development Expenses

Research and development costs are expensed as incurred and consist of salaries and benefits, lab supplies and facility costs, as well as fees paid to others that conduct certain research and development activities on the Company’s behalf. Amounts incurred in connection with collaboration and license agreements are also included in research and development expense.

Preclinical Study and Clinical Trial Accruals

The Company’s preclinical study and clinical trial accruals are a component of research and development expenses and based on patient enrollment and related costs at clinical investigator sites as well as estimates for the services received and efforts expended pursuant to contracts with multiple research institutions and clinical research organizations (“CROs”) that conduct and manage clinical trials on the Company’s behalf.

The Company estimates preclinical study and clinical trial expenses based on the services performed, pursuant to contracts with research institutions and CROs that conduct and manage preclinical studies and clinical trials on its behalf. The Company estimates these expenses based on discussions with internal clinical management personnel and external service providers as to the progress or stage of completion of trials or services and the contracted fees to be paid for such services. If the actual timing of the performance of services or the level of effort varies from the original estimates, the Company will adjust the accrual accordingly. Payments made to third parties under these arrangements in advance of the performance of the related services by the third parties are recorded as prepaid expenses until the services are rendered.

Stock-Based Compensation

The Company accounts for stock-based compensation arrangements with employees in accordance with ASC 718, Stock Compensation. Stock-based awards granted include stock options with time-based vesting, performance-based stock options and market-based stock options. ASC 718 requires the recognition of compensation expense, using a fair value-based method, for costs related to all stock-based payments. The Company’s determination of the fair value of stock options with time-based vesting on the date of grant utilizes the Black-Scholes option-pricing model, and is impacted by its common stock price as well as other variables including, but not limited to, expected term that options will remain outstanding, expected common stock price volatility over the term of the option awards, risk-free interest rates and expected dividends.

Stock-based compensation expense for performance stock options is based on the probability of achieving certain performance criteria, as defined in the individual option grant agreement. The Company estimates the number of performance options ultimately expected to vest and recognizes stock-based compensation expense for those options expected to vest when it becomes probable that the performance criteria will be met and the options vest. The Company has also granted stock options to purchase common stock that vest upon the achievement of market-based stock price targets.

The fair value of a stock-based award is recognized over the period during which an optionee is required to provide services in exchange for the option award, known as the requisite service period (usually the vesting period) on a straight-line basis. Stock-based compensation expense recognized at fair value includes the impact of estimated forfeitures. The Company estimates future forfeitures at the date of grant and revises the estimates, if necessary, in subsequent periods if actual forfeitures differ from those estimates.

Equity instruments issued to non-employees are recorded at their fair value on the measurement date and are subject to periodic adjustments as the underlying equity instruments vest. The fair value of options granted to consultants is expensed when vested. Non-employee stock-based compensation expense was not material for all periods presented.

Estimating the fair value of equity-settled awards as of the grant date using valuation models, such as the Black-Scholes option pricing model, is affected by assumptions regarding a number of complex variables. Changes in the assumptions can materially affect the fair value and ultimately how much stock-based compensation expense is recognized. These inputs are subjective and generally require significant analysis and judgment to develop.

Income Taxes

The Company provides for income taxes under the asset and liability method. Current income tax expense or benefit represents the amount of income taxes expected to be payable or refundable for the current year. Deferred income tax assets and liabilities are determined based on differences between the financial statement reporting and tax bases of assets and liabilities and net operating loss and credit carryforwards, and are measured using the enacted tax rates and laws that will be in effect when such items are expected to reverse. Deferred income tax assets are reduced, as necessary, by a valuation allowance when management determines it is more likely than not that some or all of the tax benefits will not be realized.

The Company accounts for uncertain tax positions in accordance with ASC 740-10, Accounting for Uncertainty in Income Taxes. The Company assesses all material positions taken in any income tax return, including all significant uncertain positions, in all tax years that are still subject to assessment or challenge by relevant taxing authorities. Assessing an uncertain tax position begins with the initial determination of the position’s sustainability and is measured at the largest amount of benefit that is greater than fifty percent likely of being realized upon ultimate settlement. As of each balance sheet date, unresolved uncertain tax positions must be reassessed, and the Company will determine whether (i) the factors underlying the sustainability assertion have changed and (ii) the amount of the recognized tax benefit is still appropriate. The recognition and measurement of tax benefits requires significant judgment. Judgments concerning the recognition and measurement of a tax benefit might change as new information becomes available.

The Company includes penalties and interest expense related to income taxes as a component of interest and other income, net.

Comprehensive Loss

Comprehensive loss is defined as a change in equity of a business enterprise during a period, resulting from transactions from non-owner sources. The Company had unrealized income from its available-for-sale securities during the year ended December 31, 2016, which qualified as other comprehensive income and, therefore, have been reflected in the consolidated statement of operations and comprehensive income (loss).

Net Loss per Share of Common Stock

Basic net loss per common share is calculated by dividing the net loss attributable to common stockholders by the weighted average number of common shares outstanding during the period, without consideration of potentially dilutive securities. Diluted net loss per share is computed by dividing the net loss attributable to common stockholders by the weighted average number of common shares and potentially dilutive securities outstanding for the period. For purposes of the diluted net loss per share calculation, the redeemable convertible preferred stock, common stock subject to repurchase, and stock options are considered to be potentially dilutive securities. Basic and diluted net loss attributable to common stockholders per share is presented in conformity with the two-class method required for participating securities as the convertible preferred stock is considered a participating security. The Company’s participating securities do not have a contractual obligation to share in the Company’s losses. As such, the net loss was attributed entirely to common stockholders. Because the Company has reported a net loss for all periods presented, diluted net loss per common share is the same as basic net loss per common share for those periods.

Recent Accounting Pronouncements

From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board, or FASB, or other standard setting bodies and adopted by the Company as of the specified effective date. Unless otherwise discussed, the impact of recently issued standards that are not yet effective will not have a material impact on the Company’s consolidated financial statements upon adoption. Under the Jumpstart Our Business Startups Act of 2012, as amended (the “JOBS Act”), the Company meets the definition of an emerging growth company, and has irrevocably elected to opt out of the extended transition period for complying with new or revised accounting standards pursuant to Section 107(b) of the JOBS Act.

In November 2016, the FASB issued Accounting Standard Update (“ASU”) No. 2016-18 (Topic 230), Restricted Cash, Statement of Cash Flows. This ASU 2016-18 requires that a statement of cash flows explain the change during the period in the total of cash, cash equivalents, and amounts generally described as restricted cash or restricted cash equivalents. Therefore, amounts generally described as restricted cash and restricted cash equivalents should be included with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on the statement of cash flows. ASU 2016-18 is effective for public business entities for fiscal years beginning after December 15, 2017, and interim periods within those fiscal years, with early adoption permitted. The amendments in this ASU should be applied using a retrospective transition method to each period presented. The adoption of this standard is not expected to have a material impact on the Company’s consolidated financial statements.

In August 2016, the FASB issued ASU No. 2016-15 (Topic 230), Statement of Cash Flows– Classification of Certain Cash Receipts and Cash Payments. This ASU addresses the diversity in practice in how certain cash receipts and cash payments are presented and classified in the statement of cash flows under Topic 230, Statement of Cash Flows, and other Topics. This ASU addresses eight specific cash flow issues and provides specific guidance with the objective of reducing the current and potential future diversity in practice. The amendments in this ASU are effective for public business entities for fiscal years beginning after December 15, 2017, and interim periods within those fiscal years. Early adoption is permitted, including adoption in an interim period. The Company has not determined the potential effects of this standard on its consolidated financial statements.

In March 2016, the FASB issued ASU 2016-09 (Topic 718), Compensation - Stock Compensation, which simplifies the accounting for employee share-based transactions. The amendments in this update cover such areas as the recognition of excess tax benefits and deficiencies, the classification of those excess tax benefits on the statement of cash flows, an accounting policy election for forfeitures, the amount an employer can withhold to cover income taxes and still qualify for equity classification, and the classification of those taxes paid on the statement of cash flows. ASU 2016-09 is effective for fiscal years, and interim periods within those years, beginning after December 15, 2016. The Company will adopt ASU 2016-09 in the first quarter of 2017. The Company is expecting the adoption of the ASU to have an immaterial impact on the financial statement due to the valuation allowances against deferred tax assets.

In February 2016, the FASB issued ASU No. 2016-02 (Topic 842), Leases. This ASU requires an entity to recognize assets and liabilities arising from a lease for both financing and operating leases. The ASU will also require new qualitative and quantitative disclosures to help investors and other financial statement users better understand the amount, timing, and uncertainty of cash flows arising from leases. ASU 2016-02 is effective for fiscal years beginning after December 15, 2018, with early adoption permitted. The Company has not determined the potential effects of this ASU on its consolidated financial statements.

In June 2014, the FASB issued ASU 2014-12, Accounting for Share-Based Payments When the Terms of an Award Provide That a Performance Target Could Be Achieved after the Requisite Service Period. This ASU requires that a performance target that affects vesting and could be achieved after the requisite service period be treated as a performance condition. ASU 2014-12 is effective for the Company in its first quarter of 2016. The adoption of ASU 2014-12 did not have a material impact on the Company’s consolidated financial statements and disclosures.

In May 2014, the FASB issued ASU No. 2014-09 (Topic 606), Revenue from Contracts with Customers, which supersedes the revenue recognition requirements in ASC 605, Revenue Recognition. This ASU is based on the principle that revenue is recognized to depict the transfer of goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. The ASU also requires additional disclosure about the nature, amount, timing and uncertainty of revenue and cash flows arising from customer contracts, including significant judgments and changes in judgments and assets recognized from costs incurred to obtain or fulfill a contract. In March, April, and May 2016, the FASB issued amended guidance including clarifying guidance on principal versus agent considerations, identification of performance obligations, collectability and noncash considerations. ASU 2014-09 and its amendments are effective for public entities for annual and interim periods beginning after December 15, 2017, with early adoption for fiscal 2017 permitted. The Company plans to adopt the new revenue standards in the first quarter of 2018. Since its formation, the Company has only had transactions which are recognized in revenue which relate to its Collaboration Agreement with Sanofi S.A. The Company is evaluating whether or not the identification of performance obligations and determination of their stand-alone values would remain unchanged under the new revenue standards. The Company is still assessing the impact of the adoption of the new revenue standards on its consolidated financial statements. As the Company completes its evaluation of this new standard, new information may arise that could change the Company’s current understanding of the impact to revenue recognition. Additionally, the Company will continue to monitor industry activities and any additional guidance provided by regulators, standards setters, or the accounting profession and adjust the Company’s assessment and implementation plans accordingly.

Reverse Stock Split

In October 2015, the Company’s board of directors and stockholders approved an amendment to the Company’s certificate of incorporation to effect a reverse split of shares of the Company’s issued and outstanding common stock at a 1-for-3.675 ratio and a proportional adjustment to the conversion ratio of its redeemable convertible preferred stock. The reverse stock split was effected on October 23, 2015. The par value and the authorized shares of the Company’s common stock and the par value and the authorized, issued and outstanding shares of the Company’s redeemable convertible preferred stock were not adjusted as a result of the reverse stock split. All issued and outstanding shares of common stock and common stock per share amounts and an adjustment to the redeemable convertible preferred stock ratio contained in these consolidated financial statements have been retroactively adjusted to reflect this reverse stock split for all periods presented.