Organization and Basis of Presentation (Policies)	3 Months Ended
Organization and Basis of Presentation (Policies)	Mar. 31, 2020
Summary of Significant Accounting Policies
Basis of Presentation	Basis of Presentation These condensed financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”) and pursuant to the requirements of the Securities and Exchange Commission (“SEC”) for interim reporting. As permitted under those rules and regulations, certain footnotes or other financial information that are normally required by U.S. GAAP have been condensed or omitted. These condensed financial statements have been prepared on the same basis as the Company’s most recent annual financial statements and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments necessary to present fairly the Company’s financial position at March 31, 2020 and results of operations, changes in stockholders’ equity, and cash flows for the interim periods ended March 31, 2020 and 2019. The accompanying condensed financial statements and related financial information should be read in conjunction with the audited financial statements and the related notes thereto included in the Company’s Annual Report on Form 10-K the year ended December 31, 2019. The results for the three months ended March 31, 2020, are not necessarily indicative of results to be expected for the entire year ending December 31, 2020, or any other interim period or future year.
Prior Period Errors	Prior Period Errors In connection with our review of our financial statements as of and for the six months ended June 30, 2019, we corrected errors related to the accounting for clinical trial accruals that had resulted in an overstatement of research and development expenses during the three months ended March 31, 2019 and during the year ended December 31, 2018. Specifically, management concluded that the Company’s research and development expenses recorded during the three months ended March 31, 2019 and during year ended December 31, 2018 had been overstated by $0.5 million and $3.6 million, respectively, and that the Company’s accrued expenses and other current liabilities for these periods had been overstated by the same amounts. Management analyzed the potential impact of these errors in accordance with the SEC’s Staff Accounting Bulletin No. 108, Considering the Effects of Prior Year Misstatements when Quantifying Misstatements in Current Year Financial Statements, and concluded that while the errors were significant to the Company’s financial statements as of and for the six months ended June 30, 2019, a correction of the errors would not have been material to each quarter or the full year results for 2019 and 2018 nor affect the trend of financial results. Accordingly, during the second quarter of 2019, the Company reduced accrued and other liabilities by $4.1 million and recorded a cumulative adjustment of $4.1 million in the condensed statement of operations to reduce research and development expenses.
Liquidity	Liquidity As of March 31, 2020, the Company had cash, cash equivalents and short-term investments of approximately $223.2 million. The Company believes its current available cash, cash equivalents and short-term investments will be sufficient to fund the Company’s planned expenditures and meet its obligations for at least 12 months following May 7, 2020, which is the date that these condensed financial statements are being issued.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and judgments that affect the amounts reported in the financial statements and accompanying notes thereto. On an ongoing basis, management evaluates its estimates, including those related to recognition of revenue, clinical trial accruals, contract manufacturing accruals, the fair value of assets and liabilities, 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 materially differ from those estimates.
Recent Accounting Pronouncements	Recently Adopted Accounting Pronouncements In November 2018, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2018-18, Collaborative Arrangements (Topic 808): Clarifying the Interaction between Topic 808 and Topic 606 (“ASU 2018-18”), which clarifies that certain transactions between collaborative arrangement participants should be accounted for as revenue under the FASB’s Accounting Standards Codification (“ASC”) No. 606, Revenue from Contracts with Customers (“ASC 606”) when the collaborative arrangement participant is a customer. The Company adopted ASU 2018-18 on January 1, 2020, and the adoption of this standard did not have a material impact on the Company’s financial statements. In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework— Changes to the Disclosure Requirements for Fair Value Measurement (“ASU 2018-13”), which considers cost and benefits and removes, modifies and adds disclosure requirements in Topic 820. The amendments on changes in unrealized gains and losses, the range and weighted average of significant unobservable inputs used to develop Level 3 fair value measurements and the narrative description of measurement uncertainty is to be applied prospectively for only the most recent interim or annual period presented in the initial fiscal year of adoption. All other amendments were to be applied retrospectively to all periods presented. The Company adopted ASU 2018-13 on January 1, 2020, and the adoption of this standard did not have a material impact on the Company’s financial statements. Recent Accounting Pronouncements Not Yet Adopted In December 2019, the FASB issued ASU No. 2019-12 Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes, which removes certain exceptions for intra period allocations, recognizing deferred taxes for investments and calculating income taxes in interim periods. This ASU also adds guidance to reduce complexity in certain areas, including recognizing deferred taxes for tax goodwill and allocating taxes to members of a consolidated group. The guidance is effective for the Company for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2020, with early adoption permitted. Management is currently assessing the impact of this standard on the Company’s financial statements. In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments, an amendment which modifies the measurement and recognition of credit losses for most financial assets and certain other instruments. The amendment updates the guidance for measuring and recording credit losses on financial assets measured at amortized cost by replacing the “incurred loss” model with an “expected loss” model. Accordingly, these financial assets will be presented at the net amount expected to be collected. The amendment also requires that credit losses related to available-for-sale debt securities be recorded as an allowance through net income rather than reducing the carrying amount under the current, other-than-temporary-impairment model. For smaller reporting companies the guidance is effective for fiscal years beginning after December 15, 2022, including interim periods within those fiscal years. Early adoption is permitted. Management is currently assessing the impact of this standard on the Company’s financial statements.
Fair Value Measurements	The Company’s financial instruments consist of cash and cash equivalents, short-term investments, prepaid expenses, other current assets, accounts payable, accrued expenses, and the Term Loan, as defined and discussed in Note 5. 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, accounts payable and accrued expenses 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 Term Loan, considering level 2 inputs, approximates this instrument’s 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 on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. The three-level hierarchy for the inputs to valuation techniques is briefly summarized as follows: Level 1 – Valuations are based on quoted prices in active markets for identical assets or liabilities and readily accessible by the Company at the reporting date. Examples of assets and liabilities utilizing Level 1 inputs are certain money market funds, U.S. treasuries and trading securities with quoted prices on active markets. Level 2 – Valuations based on inputs other than Level 1 that are observable, either directly or indirectly, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Examples of assets and liabilities utilizing Level 2 inputs are corporate bonds, commercial paper, certificates of deposit and over-the-counter derivatives. Level 3 – Valuations based on unobservable inputs in which there is little or no market data, which require the Company to develop its own assumptions.