Accounting Policies [Abstract] Accounting Policies [Abstract] Accounts Payable, Current Accounts payable Accretion of discount and interest expense. Accretion of Discount and Interest Expense Accretion of the discount and aggregate interest expense Accrued clinical trials current. Accrued Clinical Trials Current Accrued clinical trials Accrued contract manufacturing and non-clinical costs, current. Accrued Contract Manufacturing And Non Clinical Costs Current Accrued contract manufacturing and non-clinical costs Accrued costs, current. Accrued Costs Current Accrued costs for Shire Accrued expenses disclosure. Accrued Expenses Disclosure [Text Block] Accrued Expenses Accrued Interest Rate Percentage Accrued Interest Rate Percentage Accured Interest Accrued Liabilities, Current Accrued expenses Total accrued expenses Accrued milestones, current. Accrued Milestones Current Accrued milestones Accrued Professional Fees, Current Accrued professional service fees Accrued research and development expenses. Accrued Research And Development Expenses Policy [Text Block] Accrued Research and Development Expenses Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Accumulated depreciation Accumulated Other Comprehensive Income (Loss), Net of Tax Accumulated other comprehensive income AOCI Attributable to Parent [Member] Accumulated Other Comprehensive Income Additional Paid in Capital, Common Stock Additional paid-in capital Additional Paid-in Capital [Member] Additional Paid-In Capital APIC, Share-based Payment Arrangement, Increase for Cost Recognition Stock-based compensation Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Reconciliation of net loss to net cash used in operating activities: Share-based Payment Arrangement, Expense Stock-based compensation expense Amendment Flag Amendment Flag Amortization of premium investments. Amortization Of Premium On Investments Amortization of premium on investments Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Anti-dilutive shares of stock Antidilutive Securities [Axis] Antidilutive Securities [Axis] Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Antidilutive Securities, Name [Domain] Antidilutive Securities, Name [Domain] Area of Land Area of office space Collaborative Arrangement and Arrangement Other than Collaborative [Domain] Collaborative Arrangement and Arrangement Other than Collaborative [Domain] Asset Acquisitions [Abstract] Asset Acquisitions [Abstract] Asset Acquisitions [Abstract] Asset Acquisitions [Line Items] Asset Acquisitions [Line Items] Asset Acquisitions [Line Items] Asset Acquisitions [Table] Asset Acquisitions [Table] Asset Acquisitions [Table] Asset acquisition. Asset Acquisitions [Text Block] Asset Acquisitions Asset-backed Securities [Member] Asset Backed Securities Assets Total assets Assets [Abstract] Assets Assets, Current Total current assets Assets, Current [Abstract] Current assets: Assets, Fair Value Disclosure Fair value measurements Financial assets Assets, Fair Value Disclosure [Abstract] Financial assets: Assigned license agreement. Assigned License Agreement [Member] Assigned License Agreement Assignment and license agreement. Assignment And License Agreement [Member] Shire Agreement Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax Investments, Unrealized Gain Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax Investments, Unrealized Loss Debt Securities, Available-for-sale, Amortized Cost Investments, Amortized Cost Available-for-sale securities, debt maturities, after one to two years, fair value. Available For Sale Securities Debt Maturities After One To Two Years Fair Value One to two years Available-for-sale securities, debt maturities, after three years or more years, fair value. Available For Sale Securities Debt Maturities After Three Years Or More Years Fair Value Three years or more Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, within One Year, Fair Value Due within one year Debt Securities, Available-for-sale Investments, Estimated Fair Value Total Debt Securities, Available-for-sale, Current Short-term investments Debt Securities, Available-for-sale, Noncurrent Long-term investments Available-for-sale Securities, Gross Realized Gain (Loss) Realized gains or losses on available-for-sale investments Award Type [Axis] Award Type [Axis] Basis of Accounting, Policy [Policy Text Block] Basis of Presentation California Franchise Tax Board [Member] California Franchise Tax Board [Member] Capital Expenditures Incurred but Not yet Paid Property and equipment purchases included in accounts payable Cash Cash proceeds Cash and Cash Equivalents, at Carrying Value Cash and cash equivalents Cash and Cash Equivalents, Fair Value Disclosure Cash and cash equivalents Cash equivalents, Estimated Fair Value Cash and Cash Equivalents, Policy [Policy Text Block] Cash and Cash Equivalents Cash cash equivalents and short and long term investments. Cash Cash Equivalents And Short And Long Term Investments Cash, cash equivalents and investments Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Including Disposal Group and Discontinued Operations Cash and cash equivalents at end of period Cash and cash equivalents at beginning of period Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect Net (decrease) increase in cash and cash equivalents Cash equivalents and available for sale debt securities accumulated gross unrealized gain before tax. Cash Equivalents And Available For Sale Debt Securities Accumulated Gross Unrealized Gain Before Tax Cash equivalents and investments, Unrealized gain Cash equivalents and available for sale debt securities accumulated gross unrealized loss before tax. Cash Equivalents And Available For Sale Debt Securities Accumulated Gross Unrealized Loss Before Tax Cash equivalents and investments, Unrealized loss Cash equivalents and available for sale debt securities amortized cost basis. Cash Equivalents And Available For Sale Debt Securities Amortized Cost Basis Cash equivalents and investments, Amortized cost Cash equivalents and available for sale securities debt securities. Cash Equivalents And Available For Sale Securities Debt Securities Cash equivalents and investments, Estimated Fair Value Cash Equivalents, at Carrying Value Cash equivalents, Amortized Cost Chief Executive Officer [Member] Chief Executive Officer [Member] Class of Stock [Domain] Class of Stock [Domain] Class of Stock [Line Items] Class of Stock [Line Items] Clinical development and regulatory milestone payments payable. Clinical Development And Regulatory Milestone Payments Payable Milestone payments, payable Clinical development and regulatory milestone payments payable upon commercialization. Clinical Development And Regulatory Milestone Payments Payable Upon Commercialization Milestone payments, payable upon commercialization Clinical development and regulatory milestone payments payable upon initiation. Clinical Development And Regulatory Milestone Payments Payable Upon Initiation Milestone payments, payable upon initiation Clinical development and regulatory milestone payments payable upon regulatory approval. Clinical Development And Regulatory Milestone Payments Payable Upon Regulatory Approval Milestone payments, payable upon approval Commercial Paper [Member] Commercial Paper Commitments and Contingencies Commitments and contingencies Common Stock Capital Shares Minimum Increase In Shares Reserved For Future Issuance Common Stock Capital Shares Minimum Increase In Shares Reserved For Future Issuance Annual increase in common stock available for issuance, shares Common Stock, Capital Shares Reserved for Future Issuance Shares reserved for issuance Common stock reserved for issuance Number of common stock approved and reserved for issuance Common Stock Capital Shares Reserved For Future Issuance Annual Increase Percentage Common Stock Capital Shares Reserved For Future Issuance Annual Increase Percentage Percentage of annual increase in common stock available for issuance Common Stock Issuance Agreement [Member] Common Stock Issuance Agreement [Member] Common Stock Agreement Common stock issued in connection with asset acquisition. Common Stock Issued In Connection With Asset Acquisition Common stock issued in connection with asset acquisition Common Stock [Member] Common Stock Common Stock, Par or Stated Value Per Share Common stock, par value Common Stock, Shares Authorized Common stock, shares authorized Common Stock Shares Authorized Pre Split Common Stock Shares Authorized Pre Split Stock Split Common Stock, Shares, Issued Common stock, shares, issued Share of common stock Common Stock, Shares, Outstanding Common stock, shares, outstanding Common stock, shares, outstanding subject to repurchase. Common Stock Shares Outstanding Subject To Repurchase Common stock, subject to repurchase Common Stock Subject To Repurchase [Member] Common Stock Subject To Repurchase [Member] Common Stock Subject to Repurchase Common Stock, Value, Issued Common stock Common Stock, Voting Rights Common stock voting right Common stock, voting rights Compensation Related Costs, Policy [Policy Text Block] Stock-Based Compensation Expense Comprehensive Income (Loss), Net of Tax, Attributable to Parent Comprehensive loss Conversion [Member] Conversion [Member] Conversion [Member] Conversion of convertible note to preferred stock. Conversion of Convertible Note To Preferred Stock Conversion of convertible note to preferred stock Conversion of redeemable convertible preferred stock to common stock. Conversion Of Redeemable Convertible Preferred Stock To Common Stock Conversion of Series A redeemable convertible preferred stock into common stock on initial public offering, Shares Conversion of redeemable convertible preferred stock to common stock, value. Conversion Of Redeemable Convertible Preferred Stock To Common Stock Value Conversion of Series A redeemable convertible preferred stock into common stock on initial public offering Conversion of Stock, Amount Converted Stock converted into principal and accrued interest Conversion of Stock, Amount Issued Conversion of Series A redeemable convertible preferred stock into common stock on initial public offering Convertible Note Financing [Abstract] Convertible Note Financing [Abstract] Convertible Note Financing [Abstract] Convertible Notes Payable [Member] Convertible Notes Payable [Member] Convertible Preferred Stock [Abstract] Convertible Preferred Stock [Abstract] Convertible Preferred Stock [Abstract] Convertible Preferred Stock, Shares Issued upon Conversion Convertible preferred stock, shares issued upon conversion Number of redeemable convertible preferred stock converted into common stock Corporate Debt Securities [Member] Corporate Debt Securities Counterparty Name [Axis] Counterparty Name [Axis] Current Federal Tax Expense (Benefit) Federal Current Foreign Tax Expense (Benefit) Foreign Current Income Tax Expense (Benefit) Total current income tax expense Current Income Tax Expense (Benefit), Continuing Operations [Abstract] Current: Current State and Local Tax Expense (Benefit) State Debt Disclosure [Abstract] Debt Disclosure [Abstract] Debt Disclosure [Text Block] Convertible Note Financing Debt Instrument [Axis] Debt Instrument [Axis] Debt Instrument, Maturity Date Maturity date Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Deferred Federal Income Tax Expense (Benefit) Federal Deferred Foreign Income Tax Expense (Benefit) Foreign Deferred Income Tax Expense (Benefit) Total deferred income tax expense Deferred Income Tax Expense (Benefit), Continuing Operations [Abstract] Deferred: Deferred series a redeemable convertible preferred stock issuance costs in accounts payable. Deferred Series A Redeemable Convertible Preferred Stock Issuance Costs In Accounts Payable Deferred Series A redeemable convertible preferred stock issuance costs in accounts payable Deferred State and Local Income Tax Expense (Benefit) State Deferred Tax Assets, Gross Net deferred tax assets before valuation allowance Deferred Tax Assets, Gross [Abstract] Deferred tax assets: Deferred Tax Assets, Intangible Assets Deferred Tax Assets, Intangible Assets Intangibles Deferred Tax Assets, Net of Valuation Allowance Net deferred tax assets Deferred Tax Assets, Operating Loss Carryforwards Net operating losses Deferred Tax Assets, Other Other Deferred Tax Assets, Tax Credit Carryforwards Tax credit carryforwards Deferred Tax Assets, Tax Credit Carryforwards, Research Deferred tax assets, tax credit carryforwards, research Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals Accrued expenses Deferred Tax Assets, Valuation Allowance Valuation allowance Depreciation, Depletion and Amortization Depreciation and amortization Share-based Payment Arrangement [Abstract] Share-based Payment Arrangement [Abstract] Share-based Payment Arrangement [Text Block] Stock-Based Compensation Document And Entity Information [Abstract] Document and Entity Information [Abstract] Document and Entity Information [Abstract] Document Period End Date Document Period End Date Document Type Document Type Domestic Tax Authority [Member] Domestic Tax Authority [Member] Earnings Per Share [Abstract] Earnings Per Share [Abstract] Earnings Per Share, Basic and Diluted Net loss per common share, basic and diluted Earnings Per Share, Policy [Policy Text Block] Net Loss Per Share Effective Income Tax Rate Reconciliation, Percent Total tax benefit Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent Federal statutory income tax rate Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Percent Change in valuation allowance Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Percent State tax Effective Income Tax Rate Reconciliation, Tax Credit, Percent Tax credits Effect of Exchange Rate on Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Including Disposal Group and Discontinued Operations Effect of exchange rate on cash and cash equivalents Employee-related Liabilities, Current Accrued compensation and related benefits Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items] Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items] Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition Unrecognized stock-based compensation related to unvested stock, expected to recognize over weighted-average period Share-based Payment Arrangement, Nonvested Award, Excluding Option, Cost Not yet Recognized, Amount Total unrecognized compensation expense related to unvested restricted stock Share-based Payment Arrangement, Nonvested Award, Option, Cost Not yet Recognized, Amount Total unrecognized stock-based compensation related to unvested stock option awards granted Share-based Payment Arrangement, Option [Member] Stock Options Employee Stock Purchase Plan [Member] Employee Stock Purchase Plan [Member] Reserved for Employee Stock Purchase Plan Entity Central Index Key Entity Central Index Key Entity Emerging Growth Company Entity Emerging Growth Company Entity Ex Transition Period Entity Ex Transition Period Entity Filer Category Entity Filer Category Entity Incorporation, Date of Incorporation Date of incorporation Entity Registrant Name Entity Registrant Name Entity Small Business Entity Small Business Equity [Abstract] Equity [Abstract] Equity Component [Domain] Equity Component [Domain] Equity Method Investment, Ownership Percentage Ownership interest Fair Value, Assets, Level 1 to Level 2 Transfers, Amount Asset transfers Level 1 to Level 2 Fair Value, Assets, Level 2 to Level 1 Transfers, Amount Asset transfers Level 2 to Level 1 Fair Value Assets Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items] Fair Value Assets Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items] Fair Value Assets Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items] Fair Value, Assets Measured on Recurring Basis [Table Text Block] Summary of Financial Assets and Liabilities to Fair Value Measurements On Recurring Basis and Level of Input Measurements Asset Class [Domain] Asset Class [Domain] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Asset Class [Axis] Asset Class [Axis] Fair Value, by Balance Sheet Grouping [Table] Fair Value, by Balance Sheet Grouping [Table] Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Measurement Frequency [Axis] Measurement Frequency [Axis] Fair Value Disclosures [Abstract] Fair Value Disclosures [Abstract] Fair Value Disclosures [Text Block] Fair Value Measurements Fair Value, Inputs, Level 1 [Member] Level 1 Fair Value, Inputs, Level 2 [Member] Level 2 Fair Value, Liabilities, Level 1 to Level 2 Transfers, Amount Liabilities transfers Level 1 to Level 2 Fair Value, Liabilities, Level 2 to Level 1 Transfers, Amount Liabilities transfers Level 2 to Level 1 Measurement Frequency [Domain] Measurement Frequency [Domain] Fair Value Hierarchy and NAV [Domain] Fair Value Hierarchy and NAV [Domain] Fair Value, Recurring [Member] Fair Value, Recurring Basis Fair Value, Measurement with Unobservable Inputs Reconciliation, Liability, Transfers Into Level 3 Liability transfers into Level 3 Fair Value, Measurement with Unobservable Inputs Reconciliation, Liability, Transfers out of Level 3 Liability transfers out of Level 3 Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3 Asset transfers into Level 3 Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3 Asset transfers out of Level 3 Fair Value of Financial Instruments, Policy [Policy Text Block] Fair Value of Financial Instruments Financial Instruments Disclosure [Text Block] Financial Instruments Financial Instruments, Owned, at Fair Value [Abstract] Financial Instruments Owned At Fair Value [Abstract] Financial Liabilities Fair Value Disclosure Financial liabilities Foreign Investor [Member] Foreign Investor [Member] Foreign Investor [Member] Founder [Member] Founder [Member] Founder Future Stock Awards Or Option Grants [Member] Future Stock Awards Or Option Grants [Member] Reserved for Future Stock Awards or Option Grants General and Administrative Expense General and administrative General and Administrative Expense [Member] General and Administrative Expense