SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	12 Months Ended
Dec. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Basis of Presentation— The accompanying financial statements have been prepared in accordance with accounting principles generally accepted in the United States (U.S. GAAP). Use of Estimates—The preparation of financial statements in conformity with U.S. GAAP requires the Company to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. Actual results could differ from those estimates. Cash and Cash Equivalents—All highly liquid investments with maturities at the date of purchase of three months or less are classified as cash equivalents. There are no restrictions on cash and cash equivalents. Investments—The Company's investments are in U.S. government securities, commercial paper, corporate debt securities and asset-backed securities. All investments with maturities of greater than three months at the date of purchase and maturities of less than one year at the reporting date are classified as short-term investments, while investments with maturities of a year or more at the reporting date are classified as long-term investments. The Company has classified its investments as available-for-sale in the accompanying financial statements. Available-for-sale investments are carried at fair value, with unrealized gains and losses reported as a component of accumulated other comprehensive income (loss). Realized gains and losses on the sale of all such securities are reported in other income (expense), net and are computed using the specific identification method. All of the Company's investments are subject to a periodic impairment review. The Company recognizes an impairment charge when a decline in the fair value of investments below the cost basis is judged to be other-than-temporary and would mark the security to market through a change to the statement of operations and comprehensive loss. 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. There were no investments deemed to be impaired as of December 31, 2019. Concentration of Credit Risk and Other Risks and Uncertainties—Financial instruments that potentially subject the Company to a concentration of credit risk, consist primarily of cash, cash equivalents, short-term and long-term investments. The Company maintains deposits in federally insured financial institutions in excess of federally insured limits. Management believes that these financial institutions are financially sound, and, accordingly, minimal credit risk exists with respect to those financial institutions. The Company is exposed to credit risk in the event of default by the financial institutions holding its cash, cash equivalents, short-term and long-term investments and by the issuers of the securities to the extent recorded in the balance sheet. The Company is dependent on third-party manufacturers to supply products for research and development activities in its programs and prepare for the commercial launch of veverimer. In particular, the Company relies and expects to continue to rely on a small number of manufacturers to supply it with its requirements for the active pharmaceutical ingredient and drug product related to these programs. These programs could be adversely affected by a significant interruption in the supply of active pharmaceutical ingredients and formulated drugs. Property and Equipment—Property and equipment are stated at cost, less accumulated depreciation and amortization. Depreciation is determined using the straight-line method over the estimated useful lives of the respective assets, which is three years. Leasehold improvements are amortized using the straight-line method over the shorter of the lease term or their estimated useful economic lives. Impairment of Long-Lived Assets—Long-lived assets consist of property and equipment. The Company assesses potential impairment losses on long-lived assets used in operations when events and circumstances indicate that assets might be impaired. If such events or changes in circumstances arise, the Company compares the carrying amount of the long-lived assets to the estimated future undiscounted cash flows expected to be generated by the long-lived assets. If the estimated aggregate undiscounted cash flows are less than the carrying amount of the long-lived assets, an impairment charge, calculated as the amount by which the carrying amount of the assets exceeds the fair value of the assets, is recorded. The fair value of the long-lived assets is determined based on the estimated discounted cash flows expected to be generated from the long-lived assets. The Company has not recognized any impairment losses in the years ended December 31, 2019, 2018 and 2017. Deferred Offering Costs—The Company capitalizes certain legal, professional accounting and other third-party fees that are directly associated with in-process equity financings as deferred offering costs until such financings are consummated. After consummation of the equity financing, these costs are recorded in the statements of convertible preferred stock and stockholders’ equity (deficit) as a reduction of additional paid-in capital generated as a result of the equity financing. Clinical and Manufacturing Accruals—The Company records accruals for the estimated costs of research, nonclinical and clinical studies and manufacturing development, which are a significant component of research and development expenses. A substantial portion of the Company’s ongoing research and development activities is conducted by third-party service providers, including clinical research organizations, or CROs, and contract manufacturing organizations, or CMOs. The Company’s contracts with CROs generally include pass-through fees such as regulatory expenses, investigator fees, travel costs and other miscellaneous costs, including shipping and printing fees. The financial terms of these contracts are subject to negotiations, which vary from contract to contract and may result in payment flows that do not match the periods over which materials or services are provided to the Company under such contracts. The Company accrues the costs incurred under agreements with these third parties based on estimates of actual work completed in accordance with the respective agreements. The Company determines the estimated costs through the review of contracts and subsequent discussions with internal personnel and external service providers as to the progress or stage of completion of the services and the agreed-upon fees to be paid for such services. The Company makes significant judgments and estimates in determining the accrual balance in each reporting period. As actual costs become known, the Company adjusts its accruals. Although the Company does not expect its estimates to be materially different from amounts actually incurred, the Company’s understanding of the status and timing of services performed relative to the actual status and timing of services performed may vary and could result in the Company reporting amounts that are too high or too low in any particular period. The Company’s accrual is dependent, in part, upon the receipt of timely and accurate reporting from information provided as part of its clinical and nonclinical studies and other third-party vendors. For the three years ended December 31, 2019, 2018, and 2017, there have been no material differences from the Company’s accrued estimated expenses to the actual clinical trial and manufacturing expenses. However, variations in the assumptions used to estimate accruals, including, but not limited to the number of patients enrolled, the rate of patient enrollment, the actual services performed, and the amount of manufactured drug substance and/or drug product, and related costs may vary from the Company’s estimates, resulting in adjustments to research and development expense in future periods. Changes in these estimates that result in material changes to the Company’s accruals could materially affect its financial position and results of operations. Leases—The Company determines if an arrangement contains a lease at inception. For arrangements where the Company is the lessee, operating leases are included in operating lease right-of-use, or ROU, assets; current operating lease liabilities; and non-current operating lease liabilities on its balance sheets. The Company currently does not have any finance leases. Operating lease ROU assets and operating lease liabilities are recognized based on the present value of the future minimum lease payments over the lease term at the commencement date. ROU assets also include any initial direct costs incurred and any lease payments made on or before the lease commencement date, less lease incentives received. The Company uses its incremental borrowing rate based on the information available at the commencement date in determining the lease liabilities as the Company’s leases generally do not provide an implicit rate. The incremental borrowing rate is reevaluated upon a lease modification. The operating lease ROU asset also includes any initial direct costs and prepaid lease payments made less any lease incentives. The Company considered information available at the adoption date of Topic 842 to determine the incremental borrowing rate for leases in existence as of this date. Lease terms may include options to extend or terminate the lease when the Company is reasonably certain that the option will be exercised. Lease expense is recognized on a straight-line basis over the lease term. The Company elected to apply each of the practical expedients described in Accounting Standards Codification (ASC) Topic 842-10-65-1(f) which allow companies not to reassess: (i) whether any expired or existing agreements contain leases, (ii) the classification of any expired or existing leases, and (iii) the capitalization of initial direct costs for any existing leases. The Company also elected to apply the short-term lease measurement and recognition exemption in which ROU assets and lease liabilities are not recognized for short-term operating leases. A short-term is a lease that, at the commencement date, has a lease term of 12 months or less and does not include an option to purchase the underlying asset that the lessee is reasonably certain to exercise. Term Loan—The Company accounts for the Loan and Security Agreement, or Term Loan, with Hercules Capital, Inc., or Hercules, as a liability measured at net proceeds less debt discount and is accreted to the face value of the Term Loan over its expected term using the effective interest method. The Company considers whether there are any embedded features in its debt instruments that require bifurcation and separate accounting as derivative financial instruments pursuant to Accounting Standards Codification, or ASC, Topic 815, Derivatives and Hedging. Convertible Preferred Stock—The Company recorded all shares of convertible preferred stock at their respective fair values, net of issuance costs, on the dates of issuance. Upon the closing of the Initial Public Offering, or IPO, on July 2, 2018, the 104,225,638 shares of convertible preferred stock outstanding were automatically converted into 26,187,321 shares of common stock. Warrants—The Company issued freestanding warrants to purchase shares of common stock in connection with its Term Loan. The warrants are recorded at fair value using the Black-Scholes option pricing model. See Note 6 "Borrowings" to these financial statements for additional details. Preferred Stock Tranche Obligation—The Company entered into convertible preferred stock financings where, in addition to the initial closing, investors agreed to buy, and the Company agreed to sell, additional shares of that convertible preferred stock at a set price in the event that certain agreed milestones are achieved (a tranched financing). The Company evaluated this tranche obligation and determined that it met the definition of a freestanding instrument, and accordingly, determined the fair value of this obligation and recorded it on the balance sheet with the residual of the proceeds raised being allocated to convertible preferred stock. The preferred stock tranche obligation was revalued each reporting period with changes in the fair value of the obligation recorded as a component of other income (expense), net in the statements of operations and comprehensive loss. The preferred stock tranche obligation was revalued at settlement and the resultant fair value was then reclassified to convertible preferred stock at that time. Research and Development Expense—Research and development expense is charged to the statements of operations and comprehensive loss in the period in which they are incurred. Research and development expense consists primarily of salaries and related costs, including stock-based compensation expense, for personnel and consultants in our research and development functions; fees paid to clinical consultants, clinical trial sites and vendors, including CROs, costs related to pre-commercialization manufacturing activities including payments to CMOs and other vendors and consultants, costs related to regulatory activities, expenses related to lab supplies and services and depreciation and other allocated facility-related and overhead expenses. Nonrefundable advance payments for goods or services to be received in the future for use in research and development activities are deferred and capitalized. The capitalized amounts are expensed as the related goods are delivered or the services are performed. Stock-Based Compensation—Stock-based compensation expense represents the grant-date fair value of awards recognized on a straight-line basis or by using an accelerated attribution method for awards with performance conditions over the employee's requisite service period (generally the vesting period). The Black-Scholes option-pricing model is used to calculate stock-based compensation expense for stock option awards and shares purchased under the Employee Stock Purchase Plan, or ESPP. For restricted stock units, or RSUs, the grant-date fair value is the closing price of the Company's common stock on the date of grant as reported on The Nasdaq Global Select Market. Because stock compensation expense is an estimate of awards ultimately expected to vest, it is reduced by an estimate for future forfeitures. Forfeitures are estimated at the time of grant and revised, if necessary, in subsequent periods if actual forfeitures differ from estimates. The Company records the expense attributed to nonemployee services paid with stock option awards based on the estimated fair value of the awards determined using the Black-Scholes option pricing model. The measurement of stock-based compensation for nonemployees was previously subject to remeasurement as the options vested. As of July 1, 2018, the Company adopted ASU 2018-07, Improvements to Nonemployee Share-Based Payment Accounting, which no longer subjects nonemployee awards to remeasurement. The expense is recognized over the period during which services are received. Income Taxes—The Company accounts for income taxes using the liability method, whereby deferred tax asset and liability account balances are determined based on differences between the financial reporting and tax bases of assets and liabilities and are measured using the enacted tax rates and laws that will be in effect when the differences are expected to reverse. The Company provides a valuation allowance when it is more likely than not that some portion or all of its deferred tax assets will not be realized. The Company accounts for income tax contingencies using a benefit recognition model. If it considers that a tax position is more likely than not to be sustained upon audit, based solely on the technical merits of the position, it recognizes the benefit. The Company measures the benefit by determining the amount that is greater than 50% likely of being realized upon settlement, presuming that the tax position is examined by the appropriate taxing authority that has full knowledge of all relevant information. The Company’s policy is to recognize interest and penalties related to the underpayment of income taxes as a component of income tax expense or benefit. To date, there have been no interest or penalties charged in relation to the unrecognized tax benefits. Comprehensive Loss—Comprehensive loss is comprised of net loss and other comprehensive income (loss). Other comprehensive loss includes changes in stockholders’ equity (deficit) that are excluded from net loss, primarily unrealized gains or losses on the Company’s available-for-sale investments. These changes in stockholders' equity are reflected net of tax. Net Loss per Share—Basic net loss per share is calculated by dividing the net loss by the weighted-average number of shares of common stock outstanding during the period, without consideration for common stock equivalents. Diluted net loss per share is the same as basic net loss per share, since the effects of potentially dilutive securities are antidilutive given the net loss for each period presented. Segment Reporting—The Company manages its operations as a single operating segment for the purposes of assessing performance and making operating decisions. All of the Company's assets are maintained in the United States. Recent Accounting Pronouncements Adopted Standards In February 2016, the Financial Accounting Standards Board (FASB) issued Topic 842, which amended prior accounting standards for leases. The Company adopted Topic 842 on January 1, 2019, using the alternative modified transition method, which applies the standard as of the effective date and therefore, the Company has not applied the standard to the comparative periods presented on the Company's financial statements. The Company elected the following practical expedients when assessing the transition impact available to lessees: (i) not to reassess whether any expired or existing contracts as of January 1, 2019, are or contain leases; (ii) not to reassess the lease classification for any expired or existing leases as of January 1, 2019; and (iii) not to reassess initial direct costs for any existing leases as of January 1, 2019. As a lessee, the primary impact of the adoption of Topic 842 was the recognition of operating lease ROU assets of $2.3 million and operating lease liabilities of $2.5 million on its balance sheet as of January 1, 2019. See Note 4 "Leases" for additional details. Standards Not Yet Effective In June 2016, the FASB issued ASU 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments, or ASU 2016-13. ASU 2016-13 implements an impairment model, known as the current expected credit loss model, based on expected losses rather than incurred losses. Under the new guidance, an entity will recognize, as an allowance, its estimate of expected credit losses. The ASU is effective for interim and annual periods beginning after December 15, 2019, with early adoption permitted. The Company does not expect the adoption of ASU 2016-13 will have a significant impact on its financial statements. In September 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement, which amends ASC Topic 820, Fair Value Measurement and Disclosures, or ASU 2018-13. The FASB issued final guidance that eliminates, adds and modifies certain disclosure requirements for fair value measurements as part of its disclosure framework project. Under the ASU, entities will no longer be required to disclose the amount of transfers between Level 1 and Level 2 of the fair value hierarchy. Public companies will be required to disclose changes in unrealized gains and losses for the period included in other comprehensive income for recurring Level 3 fair value measurements held at the end of the reporting period and the range and weighted average used to develop significant unobservable inputs for Level 3 fair value measurements. ASU 2018-13 is effective for public business entities for annual reporting periods, and interim periods within those annual periods, beginning after December 15, 2019, with early adoption permitted. The Company plans to adopt this guidance on January 1, 2020. The Company does not expect the adoption of ASU 2018-13 will have a significant impact on its financial statements. In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes, or ASU 2019-12, which simplifies the accounting for income taxes. ASU 2019-12 is effective for public business entities for annual reporting periods, and interim periods within those annual periods, beginning after December 15, 2020 on a prospective basis, and early adoption is permitted. The Company does not expect the adoption of ASU 2019-12 will have a significant impact on its financial statements.

Investments—The Company's investments are in U.S. government securities, commercial paper, corporate debt securities and asset-backed securities. All investments with maturities of greater than three months at the date of purchase and maturities of less than one year at the reporting date are classified as short-term investments, while investments with maturities of a year or more at the reporting date are classified as long-term investments. The Company has classified its investments as available-for-sale in the accompanying financial statements. Available-for-sale investments are carried at fair value, with unrealized gains and losses reported as a component of accumulated other comprehensive income (loss). Realized gains and losses on the sale of all such securities are reported in other income (expense), net and are computed using the specific identification method.

All of the Company's investments are subject to a periodic impairment review. The Company recognizes an impairment charge when a decline in the fair value of investments below the cost basis is judged to be other-than-temporary and would mark the security to market through a change to the statement of operations and comprehensive loss. 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. There were no investments deemed to be impaired as of December 31, 2019.

Concentration of Credit Risk and Other Risks and Uncertainties—Financial instruments that potentially subject the Company to a concentration of credit risk, consist primarily of cash, cash equivalents, short-term and long-term investments. The Company maintains deposits in federally insured financial institutions in excess of

federally insured limits. Management believes that these financial institutions are financially sound, and, accordingly, minimal credit risk exists with respect to those financial institutions. The Company is exposed to credit risk in the event of default by the financial institutions holding its cash, cash equivalents, short-term and long-term investments and by the issuers of the securities to the extent recorded in the balance sheet.

The Company is dependent on third-party manufacturers to supply products for research and development activities in its programs and prepare for the commercial launch of veverimer. In particular, the Company relies and expects to continue to rely on a small number of manufacturers to supply it with its requirements for the active pharmaceutical ingredient and drug product related to these programs. These programs could be adversely affected by a significant interruption in the supply of active pharmaceutical ingredients and formulated drugs.

Property and Equipment—Property and equipment are stated at cost, less accumulated depreciation and amortization. Depreciation is determined using the straight-line method over the estimated useful lives of the respective assets, which is three years. Leasehold improvements are amortized using the straight-line method over the shorter of the lease term or their estimated useful economic lives.

Impairment of Long-Lived Assets—Long-lived assets consist of property and equipment. The Company assesses potential impairment losses on long-lived assets used in operations when events and circumstances indicate that assets might be impaired. If such events or changes in circumstances arise, the Company compares the carrying amount of the long-lived assets to the estimated future undiscounted cash flows expected to be generated by the long-lived assets. If the estimated aggregate undiscounted cash flows are less than the carrying amount of the long-lived assets, an impairment charge, calculated as the amount by which the carrying amount of the assets exceeds the fair value of the assets, is recorded. The fair value of the long-lived assets is determined based on the estimated discounted cash flows expected to be generated from the long-lived assets. The Company has not recognized any impairment losses in the years ended December 31, 2019, 2018 and 2017.

Deferred Offering Costs—The Company capitalizes certain legal, professional accounting and other third-party fees that are directly associated with in-process equity financings as deferred offering costs until such financings are consummated. After consummation of the equity financing, these costs are recorded in the statements of convertible preferred stock and stockholders’ equity (deficit) as a reduction of additional paid-in capital generated as a result of the equity financing.

Clinical and Manufacturing Accruals—The Company records accruals for the estimated costs of research, nonclinical and clinical studies and manufacturing development, which are a significant component of research and development expenses. A substantial portion of the Company’s ongoing research and development activities is conducted by third-party service providers, including clinical research organizations, or CROs, and contract manufacturing organizations, or CMOs. The Company’s contracts with CROs generally include pass-through fees such as regulatory expenses, investigator fees, travel costs and other miscellaneous costs, including shipping and printing fees. The financial terms of these contracts are subject to negotiations, which vary from contract to contract and may result in payment flows that do not match the periods over which materials or services are provided to the Company under such contracts. The Company accrues the costs incurred under agreements with these third parties based on estimates of actual work completed in accordance with the respective agreements. The Company determines the estimated costs through the review of contracts and subsequent discussions with internal personnel and external service providers as to the progress or stage of completion of the services and the agreed-upon fees to be paid for such services.

The Company makes significant judgments and estimates in determining the accrual balance in each reporting period. As actual costs become known, the Company adjusts its accruals. Although the Company does not expect its estimates to be materially different from amounts actually incurred, the Company’s understanding of the status and timing of services performed relative to the actual status and timing of services performed may vary and could result in the Company reporting amounts that are too high or too low in any particular period. The Company’s accrual is dependent, in part, upon the receipt of timely and accurate reporting from information provided as part of its clinical and nonclinical studies and other third-party vendors. For the three years ended December 31, 2019, 2018, and 2017, there have been no material differences from the Company’s accrued estimated expenses to the actual clinical trial and manufacturing expenses. However, variations in the assumptions used to estimate accruals, including, but not limited to the number of patients enrolled, the rate of patient enrollment, the actual services performed, and the amount of manufactured drug substance and/or drug product, and related costs may vary from the Company’s estimates, resulting in adjustments to research and development expense in future periods. Changes in these estimates that result in material changes to the Company’s accruals could materially affect its financial position and results of operations.

Leases—The Company determines if an arrangement contains a lease at inception. For arrangements where the Company is the lessee, operating leases are included in operating lease right-of-use, or ROU, assets; current operating lease liabilities; and non-current operating lease liabilities on its balance sheets. The Company currently does not have any finance leases.

Operating lease ROU assets and operating lease liabilities are recognized based on the present value of the future minimum lease payments over the lease term at the commencement date. ROU assets also include any initial direct costs incurred and any lease payments made on or before the lease commencement date, less lease incentives received. The Company uses its incremental borrowing rate based on the information available at the commencement date in determining the lease liabilities as the Company’s leases generally do not provide an implicit rate. The incremental borrowing rate is reevaluated upon a lease modification. The operating lease ROU asset also includes any initial direct costs and prepaid lease payments made less any lease incentives. The Company considered information available at the adoption date of Topic 842 to determine the incremental borrowing rate for leases in existence as of this date. Lease terms may include options to extend or terminate the lease when the Company is reasonably certain that the option will be exercised. Lease expense is recognized on a straight-line basis over the lease term.

The Company elected to apply each of the practical expedients described in Accounting Standards Codification (ASC) Topic 842-10-65-1(f) which allow companies not to reassess: (i) whether any expired or existing agreements contain leases, (ii) the classification of any expired or existing leases, and (iii) the capitalization of initial direct costs for any existing leases. The Company also elected to apply the short-term lease measurement and recognition exemption in which ROU assets and lease liabilities are not recognized for short-term operating leases. A short-term is a lease that, at the commencement date, has a lease term of 12 months or less and does not include an option to purchase the underlying asset that the lessee is reasonably certain to exercise.

Term Loan—The Company accounts for the Loan and Security Agreement, or Term Loan, with Hercules Capital, Inc., or Hercules, as a liability measured at net proceeds less debt discount and is accreted to the face value of the Term Loan over its expected term using the effective interest method. The Company considers whether there are any embedded features in its debt instruments that require bifurcation and separate accounting as derivative financial instruments pursuant to Accounting Standards Codification, or ASC, Topic 815, Derivatives and Hedging.

Convertible Preferred Stock—The Company recorded all shares of convertible preferred stock at their respective fair values, net of issuance costs, on the dates of issuance. Upon the closing of the Initial Public Offering, or IPO, on July 2, 2018, the 104,225,638 shares of convertible preferred stock outstanding were automatically converted into 26,187,321 shares of common stock.

Preferred Stock Tranche Obligation—The Company entered into convertible preferred stock financings where, in addition to the initial closing, investors agreed to buy, and the Company agreed to sell, additional shares of that convertible preferred stock at a set price in the event that certain agreed milestones are achieved (a tranched financing). The Company evaluated this tranche obligation and determined that it met the definition of a freestanding instrument, and accordingly, determined the fair value of this obligation and recorded it on the balance sheet with the residual of the proceeds raised being allocated to convertible preferred stock. The preferred stock tranche obligation was revalued each reporting period with changes in the fair value of the obligation recorded as a component of other income (expense), net in the statements of operations and comprehensive loss. The preferred stock tranche obligation was revalued at settlement and the resultant fair value was then reclassified to convertible preferred stock at that time.

Research and Development Expense—Research and development expense is charged to the statements of operations and comprehensive loss in the period in which they are incurred. Research and development expense consists primarily of salaries and related costs, including stock-based compensation expense, for personnel and consultants in our research and development functions; fees paid to clinical consultants, clinical trial sites and vendors, including CROs, costs related to pre-commercialization manufacturing activities including payments to CMOs and other vendors and consultants, costs related to regulatory activities, expenses related to lab supplies and services and depreciation and other allocated facility-related and overhead expenses. Nonrefundable advance payments for goods or services to be received in the future for use in research and development activities are

Stock-Based Compensation—Stock-based compensation expense represents the grant-date fair value of awards recognized on a straight-line basis or by using an accelerated attribution method for awards with performance conditions over the employee's requisite service period (generally the vesting period). The Black-Scholes option-pricing model is used to calculate stock-based compensation expense for stock option awards and shares purchased under the Employee Stock Purchase Plan, or ESPP. For restricted stock units, or RSUs, the grant-date fair value is the closing price of the Company's common stock on the date of grant as reported on The Nasdaq Global Select Market. Because stock compensation expense is an estimate of awards ultimately expected to vest, it is reduced by an estimate for future forfeitures. Forfeitures are estimated at the time of grant and revised, if necessary, in subsequent periods if actual forfeitures differ from estimates.

The Company records the expense attributed to nonemployee services paid with stock option awards based on the estimated fair value of the awards determined using the Black-Scholes option pricing model. The measurement of stock-based compensation for nonemployees was previously subject to remeasurement as the options vested. As of July 1, 2018, the Company adopted ASU 2018-07, Improvements to Nonemployee Share-Based Payment Accounting, which no longer subjects nonemployee awards to remeasurement. The expense is recognized over the period during which services are received.

Income Taxes—The Company accounts for income taxes using the liability method, whereby deferred tax asset and liability account balances are determined based on differences between the financial reporting and tax bases of assets and liabilities and are measured using the enacted tax rates and laws that will be in effect when the differences are expected to reverse. The Company provides a valuation allowance when it is more likely than not that some portion or all of its deferred tax assets will not be realized.

The Company accounts for income tax contingencies using a benefit recognition model. If it considers that a tax position is more likely than not to be sustained upon audit, based solely on the technical merits of the position, it recognizes the benefit. The Company measures the benefit by determining the amount that is greater than 50% likely of being realized upon settlement, presuming that the tax position is examined by the appropriate taxing authority that has full knowledge of all relevant information. The Company’s policy is to recognize interest and penalties related to the underpayment of income taxes as a component of income tax expense or benefit. To date, there have been no interest or penalties charged in relation to the unrecognized tax benefits.

Comprehensive Loss—Comprehensive loss is comprised of net loss and other comprehensive income (loss). Other comprehensive loss includes changes in stockholders’ equity (deficit) that are excluded from net loss, primarily unrealized gains or losses on the Company’s available-for-sale investments. These changes in stockholders' equity are reflected net of tax.

Net Loss per Share—Basic net loss per share is calculated by dividing the net loss by the weighted-average number of shares of common stock outstanding during the period, without consideration for common stock equivalents. Diluted net loss per share is the same as basic net loss per share, since the effects of potentially dilutive securities are antidilutive given the net loss for each period presented.

In February 2016, the Financial Accounting Standards Board (FASB) issued Topic 842, which amended prior accounting standards for leases. The Company adopted Topic 842 on January 1, 2019, using the alternative modified transition method, which applies the standard as of the effective date and therefore, the Company has not applied the standard to the comparative periods presented on the Company's financial statements.

In June 2016, the FASB issued ASU 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments, or ASU 2016-13. ASU 2016-13 implements an impairment model, known as the current expected credit loss model, based on expected losses rather than incurred losses. Under the new guidance, an entity will recognize, as an allowance, its estimate of expected credit losses. The ASU is effective for interim and annual periods beginning after December 15, 2019, with early adoption permitted. The Company does not expect the adoption of ASU 2016-13 will have a significant impact on its financial statements.

In September 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement, which amends ASC Topic 820, Fair Value Measurement and Disclosures, or ASU 2018-13. The FASB issued final guidance that eliminates, adds and modifies certain disclosure requirements for fair value measurements as part of its disclosure framework project. Under the ASU, entities will no longer be required to disclose the amount of transfers between Level 1 and Level 2 of the fair value hierarchy. Public companies will be required to disclose changes in unrealized gains and losses for the period included in other comprehensive income for recurring Level 3 fair value measurements held at the end of the reporting period and the range and weighted average used to develop significant unobservable inputs for Level 3 fair value measurements. ASU 2018-13 is effective for public business entities for annual reporting periods, and interim periods within those annual periods, beginning after December 15, 2019, with early adoption permitted. The Company plans to adopt this guidance on January 1, 2020. The Company does not expect the adoption of ASU 2018-13 will have a significant impact on its financial statements.

In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes, or ASU 2019-12, which simplifies the accounting for income taxes. ASU 2019-12 is effective for public business entities for annual reporting periods, and interim periods within those annual periods, beginning after December 15, 2020 on a prospective basis, and early adoption is permitted. The Company does not expect the adoption of ASU 2019-12 will have a significant impact on its financial statements.