Entity Central Index Key Cover [Abstract] Document Type Document Type Amendment Flag Amendment Flag Document Period End Date Document Period End Date Document Fiscal Year Focus Document Fiscal Year Focus Document Fiscal Period Focus Document Fiscal Period Focus Trading Symbol Trading Symbol Entity Registrant Name Entity Registrant Name Entity Central Index Key Entity Current Reporting Status Entity Current Reporting Status Entity Interactive Data Current Entity Interactive Data Current Current Fiscal Year End Date Current Fiscal Year End Date Entity Filer Category Entity Filer Category Entity Small Business Entity Small Business Entity Shell Company Entity Shell Company Entity Emerging Growth Company Entity Emerging Growth Company Entity Ex Transition Period Entity Ex Transition Period Entity Common Stock, Shares Outstanding Entity Common Stock Shares Outstanding Title of 12(b) Security Security12b Title Security Exchange Name Security Exchange Name Entity File Number Entity File Number Entity Incorporation, State or Country Code Entity Incorporation State Country Code Entity Tax Identification Number Entity Tax Identification Number Entity Address, Address Line One Entity Address Address Line1 Entity Address, Address Line Two Entity Address Address Line2 Entity Address, City or Town Entity Address City Or Town Entity Address, State or Province Entity Address State Or Province Entity Address, Postal Zip Code Entity Address Postal Zip Code City Area Code City Area Code Local Phone Number Local Phone Number Document Quarterly Report Document Quarterly Report Document Transition Report Document Transition Report Deferred offering costs non current. Statement Of Financial Position [Abstract] Statement [Table] Statement [Table] Class of Stock Statement Class Of Stock [Axis] Class of Stock Class Of Stock [Domain] Series A redeemable convertible preferred stock. Series A Redeemable Convertible Preferred Stock Series A Redeemable Convertible Preferred Stock [Member] Series B redeemable convertible preferred stock. Series B Redeemable Convertible Preferred Stock Series B Redeemable Convertible Preferred Stock [Member] Statement [Line Items] Statement [Line Items] Assets Assets [Abstract] Current assets Assets Current [Abstract] Cash and cash equivalents Cash And Cash Equivalents At Carrying Value Short-term marketable securities Marketable Securities Current Prepaid expenses and other current assets Prepaid Expense And Other Assets Current Total current assets Assets Current Restricted cash Restricted Cash Noncurrent Property and equipment, net Property Plant And Equipment Net Deferred offering costs Deferred Offering Costs Non Current Right-of-use assets Operating Lease Right Of Use Asset Other non-current assets Other Assets Noncurrent Total assets Assets Liabilities, Redeemable Convertible Preferred Stock and Stockholders’ Equity (Deficit) Liabilities And Stockholders Equity [Abstract] Current liabilities Liabilities Current [Abstract] Accounts payable Accounts Payable Current Accrued liabilities Accrued Liabilities Current Deferred rent Deferred Rent Credit Current Lease liabilities Operating Lease Liability Current Other current liabilities Other Liabilities Current Total current liabilities Liabilities Current Deferred rent Deferred Rent Credit Noncurrent Long-term lease liabilities Operating Lease Liability Noncurrent Other non-current liabilities Other Liabilities Noncurrent Total liabilities Liabilities Commitments and contingencies (Note 5) Commitments And Contingencies Temporary equity, value Temporary Equity Carrying Amount Attributable To Parent Stockholder’s equity (deficit) Stockholders Equity [Abstract] Preferred stock, $0.0001 par value, 10,000,000 shares authorized as of September 30, 2019 and no shares authorized as of December 31, 2018; no shares issued and outstanding as of September 30, 2019 and December 31, 2018 Preferred Stock Value Common stock, $0.0001 par value, 300,000,000 shares authorized as of September 30, 2019 and 170,800,000 shares authorized as of December 31, 2018; 20,328,242 and 1,335,690 shares issued and outstanding as of September 30, 2019 and December 31, 2018 Common Stock Value Additional paid-in capital Additional Paid In Capital Common Stock Accumulated other comprehensive income (loss) Accumulated Other Comprehensive Income Loss Net Of Tax Accumulated deficit Retained Earnings Accumulated Deficit Total stockholders’ equity (deficit) Stockholders Equity Total liabilities, redeemable convertible preferred stock and stockholders’ equity (deficit) Liabilities And Stockholders Equity Redeemable convertible preferred stock, par value Temporary Equity Par Or Stated Value Per Share Redeemable convertible preferred stock, shares authorized Temporary Equity Shares Authorized Redeemable convertible preferred stock, shares issued Temporary Equity Shares Issued Redeemable convertible preferred stock, shares outstanding Temporary Equity Shares Outstanding Redeemable convertible preferred stock, liquidation value Temporary Equity Liquidation Preference Preferred stock, par value Preferred Stock Par Or Stated Value Per Share Preferred stock, shares authorized Preferred Stock Shares Authorized Preferred stock, shares issued Preferred Stock Shares Issued Preferred stock, shares outstanding Preferred Stock Shares Outstanding Common stock, par value Common Stock Par Or Stated Value Per Share Common stock, shares authorized Common Stock Shares Authorized Common stock, shares issued Common Stock Shares Issued Common stock, shares outstanding Common Stock Shares Outstanding Income Statement [Abstract] Operating expenses Operating Expenses [Abstract] Research and development Research And Development Expense General and administrative General And Administrative Expense Total operating expenses Operating Expenses Loss from operations Operating Income Loss Interest income Investment Income Interest Other income (expense), net Other Nonoperating Income Expense Net loss Net Income Loss Change in unrealized gains (losses) on marketable securities Other Comprehensive Income Loss Available For Sale Securities Adjustment Net Of Tax Comprehensive loss Comprehensive Income Net Of Tax Net loss per share attributable to common stockholders, basic and diluted Earnings Per Share Basic And Diluted Weighted average number of shares outstanding, basic and diluted Weighted Average Number Of Share Outstanding Basic And Diluted Temporary equity stock issued during period shares new issues. Temporary equity conversion of redeemable convertible preferred stock into common stock. Statement Of Stockholders Equity [Abstract] Equity Components Statement Equity Components [Axis] Equity Component Equity Component [Domain] Common Stock Common Stock [Member] Additional Paid-In Capital Additional Paid In Capital [Member] Accumulated Other Comprehensive Income (Loss) Accumulated Other Comprehensive Income [Member] Accumulated Deficit Retained Earnings [Member] Redeemable Convertible Preferred Stock Redeemable Convertible Preferred Stock [Member] Collaborative Arrangement and Arrangement Other than Collaborative Type Of Arrangement [Axis] Collaborative Arrangement and Arrangement Other than Collaborative Arrangements And Nonarrangement Transactions [Member] License agreement. License Agreement License Agreement [Member] Redeemable convertible preferred stock, beginning balance Redeemable convertible preferred stock, beginning balance, shares Conversion of redeemable convertible preferred stock into common stock Temporary Equity Conversion Of Redeemable Convertible Preferred Stock In To Common Stock Temporary equity conversion of redeemable convertible preferred stock in to common stock shares. Conversion of redeemable convertible preferred stock into common stock, shares Temporary Equity Conversion Of Redeemable Convertible Preferred Stock In To Common Stock Shares Issuance of redeemable convertible preferred stock, value Temporary Equity Stock Issued During Period Value New Issues Issuance of redeemable convertible preferred stock, shares Temporary Equity Stock Issued During Period Shares New Issues Redeemable convertible preferred stock, ending balance Redeemable convertible preferred stock, ending balance, shares Adjustments to additional paid in capital, vesting of early exercise of shares. Stock issued during period, shares, early exercised common stock options. Stock issued during period, value, early exercised common stock options. Beginning balance Beginning balance, shares Shares Outstanding Conversion of redeemable convertible preferred stock into common stock Stock Issued During Period Value Conversion Of Convertible Securities Conversion of redeemable convertible preferred stock into common stock, shares Stock Issued During Period Shares Conversion Of Convertible Securities Issuance of common stock upon initial public offering, net of issuance cost Stock Issued During Period Value New Issues Issuance of common stock upon initial public offering, net of issuance cost, shares Stock Issued During Period Shares New Issues Issuance of common stock upon exercise of stock options Stock Issued During Period Value Stock Options Exercised Issuance of common stock upon exercise of stock options, shares Stock Issued During Period Shares Stock Options Exercised Early exercised common stock options Stock Issued During Period Value Early Exercised Common Stock Options Early exercised common stock options, shares Stock Issued During Period Shares Early Exercised Common Stock Options Repurchase of early exercised shares Stock Repurchased During Period Value Repurchase of early exercised shares, shares Stock Repurchased During Period Shares Vesting of early exercised common stock options and restricted stock Adjustments To Additional Paid In Capital Vesting Of Early Exercise Of Shares Vesting of early exercised common stock options and restricted stock. Vesting of early exercised common stock options and restricted stock, shares Vesting Of Early Exercised Common Stock Options And Restricted Stock Stock-based compensation Adjustments To Additional Paid In Capital Sharebased Compensation Requisite Service Period Recognition Value Other comprehensive income (loss) Other Comprehensive Income Loss Net Of Tax Portion Attributable To Parent Net loss Ending balance Ending balance, shares Redeemable convertible preferred stock liability. Stock issuance cost Payments Of Stock Issuance Costs Redeemable convertible preferred stock liability Redeemable Convertible Preferred Stock Liability Issuance of temporary equity stock pursuant to license agreement. Change in fair value of redeemable convertible preferred stock liability. Landlord contributions for leasehold improvements. Increase (decrease) in operating lease right-of-use assets. Increase (decrease) in operating lease liabilities. Proceeds from maturity of marketable securities. Proceeds from sale of marketable securities. Vesting of early exercised options and restricted stock. Extinguishment of redeemable convertible preferred stock liability. Conversion of redeemable convertible preferred stock into common stock. Statement Of Cash Flows [Abstract] Cash flows from operating activities Net Cash Provided By Used In Operating Activities [Abstract] Net loss Profit Loss Adjustments to reconcile net loss to net cash used in operating activities Adjustments To Reconcile Net Income Loss To Cash Provided By Used In Operating Activities [Abstract] Depreciation and amortization Depreciation Depletion And Amortization Net amortization of premiums and discounts on marketable securities Accretion Amortization Of Discounts And Premiums Investments Stock-based compensation Share Based Compensation Issuance of Series B redeemable convertible preferred stock pursuant to license agreement Issuance Of Temporary Equity Stock Pursuant To License Agreement Change in fair value of redeemable convertible preferred stock liability Change In Fair Value Of Redeemable Convertible Preferred Stock Liability Landlord contributions for leasehold improvements Landlord Contributions For Leasehold Improvements Loss (gain) on sale of property and equipment Gain Loss On Sale Of Property Plant Equipment Gain on sales of marketable securities Gain On Sale Of Investments Changes in assets and liabilities Increase Decrease In Operating Capital [Abstract] Prepaid expenses and other assets Increase Decrease In Prepaid Deferred Expense And Other Assets Right-of-use assets Increase Decrease In Operating Lease Right Of Use Assets Accounts payable Increase Decrease In Accounts Payable Accrued and other liabilities Increase Decrease In Accrued Liabilities And Other Operating Liabilities Deferred rent Increase Decrease In Deferred Liabilities Lease liabilities Increase Decrease In Operating Lease Liabilities Net cash used in operating activities Net Cash Provided By Used In Operating Activities Cash flows from investing activities Net Cash Provided By Used In Investing Activities [Abstract] Purchases of property and equipment, net Payments To Acquire Property Plant And Equipment Purchases of marketable securities Payments To Acquire Marketable Securities Maturities of marketable securities Proceeds From Maturity Of Marketable Securities Sales of marketable securities Proceeds From Sale Of Marketable Securities Net cash used in investing activities Net Cash Provided By Used In Investing Activities Cash flows from financing activities Net Cash Provided By Used In Financing Activities [Abstract] Proceeds from issuance of redeemable convertible preferred stock, net of issuance costs Proceeds From Issuance Of Redeemable Convertible Preferred Stock Proceeds from issuance of common stock in initial public offering, net of issuance costs Proceeds From Issuance Initial Public Offering Proceeds from exercise of common stock options Proceeds From Stock Options Exercised Net cash provided by financing activities Net Cash Provided By Used In Financing Activities Net increase in cash, cash equivalents and restricted cash Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents Period Increase Decrease Including Exchange Rate Effect Cash, cash equivalents and restricted cash, at beginning of period Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents Cash, cash equivalents and restricted cash, at end of period Reconciliation of cash, cash equivalents and restricted cash Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents [Abstract] Restricted cash Restricted Cash Supplemental disclosure of cash flow information: Supplemental Cash Flow Information [Abstract] Cash paid for income taxes Income Taxes Paid Net Cash paid for interest Interest Paid Net Supplemental non-cash investing and financing activities: Cash Flow Noncash Investing And Financing Activities Disclosure [Abstract] Issuance of Series B redeemable convertible preferred stock pursuant to license agreement Stock Issued1 Vesting of early exercised options and restricted stock Vesting Of Early Exercised Options And Restricted Stock Purchases of property and equipment in accounts payable and accrued liabilities Capital Expenditures Incurred But Not Yet Paid Extinguishment of redeemable convertible preferred stock liability Extinguishment Of Redeemable Convertible Preferred Stock Liability Conversion of redeemable convertible preferred stock into common stock Conversion Of Redeemable Convertible Preferred Stock In To Common Stock Organization Consolidation And Presentation Of Financial Statements [Abstract] Organization Organization Consolidation And Presentation Of Financial Statements Disclosure [Text Block] Accounting Policies [Abstract] Summary of Significant Accounting Policies Significant Accounting Policies [Text Block] Fair value measurements and short-term marketable securities. Fair Value Disclosures [Abstract] Fair Value Measurements and Short-Term Marketable Securities Fair Value Measurements And Short Term Marketable Securities [Text Block] Balance Sheet Related Disclosures [Abstract] Balance Sheet Components Supplemental Balance Sheet Disclosures [Text Block] Leases [Abstract] Leases, Lease Commitments and Contingencies Commitments And Contingencies Disclosure [Text Block] Income Tax Disclosure [Abstract] Income Taxes Income Tax Disclosure [Text Block] Temporary equity disclosure. Temporary Equity Disclosure [Abstract] Redeemable Convertible Preferred Stock Temporary Equity Disclosure [Text Block] Stockholders Equity Note [Abstract] Common Stock Stockholders Equity Note Disclosure [Text Block] Disclosure Of Compensation Related Costs Sharebased Payments [Abstract] Stock-Based Compensation Disclosure Of Compensation Related Costs Share Based Payments [Text Block] Earnings Per Share [Abstract] Net Loss Per Share Attributable to Common Stockholders Earnings Per Share [Text Block] Related Party Transactions [Abstract] Related Party Transactions Related Party Transactions Disclosure [Text Block] Basis of Presentation Basis Of Accounting Policy Policy [Text Block] Reverse stock split. Reverse Stock Split Reverse Stock Split Policy [Text Block] Use of Estimates Use Of Estimates Risks and uncertainties. Risks and Uncertainties Risks And Uncertainties Policy [Text Block] Concentration of Credit Risk Concentration Risk Credit Risk Deferred Initial Public Offering Costs Deferred Charges Policy [Text Block] Leases Lessee Leases Policy [Text Block] Net Loss per Share Attributable to Common Stockholders Earnings Per Share Policy [Text Block] Recently Adopted Accounting Pronouncements New Accounting Pronouncements Policy Policy [Text Block] Fair value measurements and short-term marketable securities policy. Fair Value Measurements and Short-Term Marketable Securities Fair Value Measurements And Short Term Marketable Securities Policy [Text Block] Share Based Compensation Forfeiture Share Based Compensation Forfeitures Policy [Text Block] Schedule of Financial Assets Measured and Recognized at Fair Value Fair Value By Balance Sheet Grouping [Text Block] Summary of Property and Equipment, Net Property Plant And Equipment [Text Block] Summary of Accrued Liabilities Schedule Of Accrued Liabilities Table [Text Block] Schedule of Future Minimum Lease Payments Under Non-cancelable Operating Leases Schedule Of Future Minimum Rental Payments For Operating Leases Table [Text Block] Schedule of Maturities of Operating Lease Liabilities Lessee Operating Lease Liability Maturity Table [Text Block] Schedule of Issued and Outstanding Redeemable Convertible Preferred Stock and Principal Terms Temporary Equity Table [Text Block] Schedule of common stock reserved for future issuance. Schedule of Number of Common Stock Reserved for Future Issuance Schedule Of Common Stock Reserved For Future Issuance Table [Text Block] Summary of Stock-Based Compensation Expense Schedule Of Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Text Block] Summary of Activity under Equity Incentive Plans Schedule Of Share Based Compensation Stock Options Activity Table [Text Block] Assumptions Used to Calculate Fair Values of Options Schedule Of Share Based Payment Award Stock Options Valuation Assumptions Table [Text Block] Summary of Restricted Stock Activity Schedule Of Nonvested Restricted Stock Units Activity Table [Text Block] Computation of Basic and Diluted Net Loss Per Share Attributable to Common Stockholders Schedule Of Earnings Per Share Basic And Diluted Table [Text Block] Schedule of Outstanding Shares of Potentially Dilutive Securities Excluded From the Computation of Diluted Net Loss Per Share Schedule Of Antidilutive Securities Excluded From Computation Of Earnings Per Share [Text Block] Subsidiary Or Equity Method Investee Sale Of Stock By Subsidiary Or Equity Investee [Table] Subsidiary Or Equity Method Investee Sale Of Stock By Subsidiary Or Equity Investee [Table] Sale of Stock Subsidiary Sale Of Stock [Axis] Sale of Stock Sale Of Stock Name Of Transaction [Domain] IPO I P O [Member] Over Allotment Option Over Allotment Option [Member] Subsidiary Sale Of Stock [Line Items] Subsidiary Sale Of Stock [Line Items] Common stock, shares issued Common stock, price per share Shares Issued Price Per Share Accumulated deficit Cash, cash equivalents and short-term marketable securities Cash Cash Equivalents And Short Term Investments Summary of significant accounting policies. Summary of significant accounting policies. Summary Of Significant Accounting Policies [Table] Summary Of Significant Accounting Policies [Table] Summary Of Significant Accounting Policies [Line Items] Summary Of Significant Accounting Policies [Line Items] Reverse stock split ratio Stockholders Equity Note Stock Split Conversion Ratio1 Deferred offering costs Deferred Offering Costs Operating lease liabilities Operating Lease Liability Deferred rent Deferred Rent Credit Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Table] Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Table] Investment Type Investment Type [Axis] Investments Investment Type Categorization [Member] U.S. Government Securities U S Government Agencies Debt Securities [Member] Corporate Bonds Corporate Bond Securities [Member] Commercial Paper Commercial Paper [Member] Commercial Paper Commercial Paper Not Included With Cash And Cash Equivalents [Member] Asset-Backed Securities Asset Backed Securities [Member] Money Market Funds Money Market Funds [Member] Fair Value Hierarchy and NAV Fair Value By Fair Value Hierarchy Level [Axis] Fair Value Hierarchy and NAV Fair Value Measurements Fair Value Hierarchy [Domain] Level 1 Fair Value Inputs Level1 [Member] Level 2 Fair Value Inputs Level2 [Member] Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] Marketable securities, amortized cost Available For Sale Debt Securities Amortized Cost Basis Marketable securities, gross unrealized gains Available For Sale Debt Securities Accumulated Gross Unrealized Gain Before Tax Marketable securities, gross unrealized losses Available For Sale Debt Securities Accumulated Gross Unrealized Loss Before Tax Marketable securities, estimated fair value Available For Sale Securities Debt Securities Money market funds, amortized Cost Cash Equivalents At Carrying Value Money market funds, estimated Fair Value Cash And Cash Equivalents Fair Value Disclosure Amortized Cost Investment Owned At Cost Estimated Fair Value Investments Fair Value Disclosure Marketable securities remaining maturity period. Statistical Measurement Range [Axis] Statistical Measurement Range [Member] Maximum Maximum [Member] Minimum Minimum [Member] Financial liabilities recognized at fair value Financial Liabilities Fair Value Disclosure Marketable securities remaining maturity period Marketable Securities Remaining Maturity Period Schedule Of Property Plant And Equipment [Table] Schedule Of Property Plant And Equipment [Table] Property, Plant and Equipment, Type Property Plant And Equipment By Type [Axis] Property, Plant and Equipment, Type Property Plant And Equipment Type [Domain] Laboratory equipment. Laboratory Equipment Laboratory Equipment [Member] Computer Equipment Computer Equipment [Member] Software Software Development [Member] Leasehold Improvements Leasehold Improvements [Member] Furniture and Fixtures Furniture And Fixtures [Member] Property Plant And Equipment [Line Items] Property Plant And Equipment [Line Items] Total property and equipment Property Plant And Equipment Gross Less: Accumulated depreciation and amortization Accumulated Depreciation Depletion And Amortization Property Plant And Equipment Property and equipment, net Property and equipment net, useful life Property Plant And Equipment Useful Life Property and equipment net, useful life Property Plant And Equipment Estimated Useful Lives Depreciation and amortization expense Depreciation And Amortization Accrued research and development expenses current. Accrued salaries and benefits Employee Related Liabilities Current Accrued research and development expenses Accrued Research And Development Expenses Current Legal and professional fees Accrued Professional Fees Current Other Other Accrued Liabilities Current Accrued liabilities Schedule Of Operating Leased Assets [Table] Schedule Of Operating Leased Assets [Table] Geographical Statement Geographical [Axis] Geographical Segment Geographical [Domain] South San Francisco, California. South San Francisco, California South San Francisco California [Member] San Diego, California. San Diego, California San Diego California [Member] Finite-Lived Intangible Assets by Major Class Finite Lived Intangible Assets By Major Class [Axis] Finite-Lived Intangible Assets, Major Class Name Finite Lived Intangible Assets Major Class Name [Domain] Lease Agreement Lease Agreements [Member] Laboratory and office facilities. Laboratory and Office Facilities Laboratory And Office Facilities [Member] New lease agreement. Amendment of Lease Agreement New Lease Agreement [Member] Operating Leased Assets [Line Items] Operating Leased Assets [Line Items] Lease expiration date Lease Expiration Date1 Tenant improvement allowance provided by landlord. Tenant improvement allowance Tenant Improvement Allowance Provided Rent expense Operating Leases Rent Expense Net Deferred rent 2019 Operating Leases Future Minimum Payments Remainder Of Fiscal Year 2020 Operating Leases Future Minimum Payments Due In Two Years 2021 Operating Leases Future Minimum Payments Due In Three Years 2022 Operating Leases Future Minimum Payments Due In Four Years 2023 Operating Leases Future Minimum Payments Due In Five Years Thereafter Operating Leases Future Minimum Payments Due Thereafter Total lease payments Operating Leases Future Minimum Payments Due Remaining fiscal 2019 Lessee Operating Lease Liability Payments Remainder Of Fiscal Year 2020 Lessee Operating Lease Liability Payments Due Year Two 2021 Lessee Operating Lease Liability Payments Due Year Three 2022 Lessee Operating Lease Liability Payments Due Year Four 2023 Lessee Operating Lease Liability Payments Due Year Five Thereafter Lessee Operating Lease Liability Payments Due After Year Five Total lease payments Lessee Operating Lease Liability Payments Due Less: Interest Lessee Operating Lease Liability Undiscounted Excess Amount Current lease liabilities Total lease liabilities Operating lease expense Operating Lease Expense Operating lease, remaining lease term Operating Lease Weighted Average Remaining Lease Term1 Operating lease, discount rate Operating Lease Weighted Average Discount Rate Percent Cash paid included in operating lease liabilities included in cash flow from operating activities Operating Lease Payments Federal or state income tax provision or benefit Income Tax Expense Benefit Temporary equity original issue price per share. Temporary Equity By Class Of Stock [Table] Temporary Equity By Class Of Stock [Table] Temporary Equity [Line Items] Temporary Equity [Line Items] Redeemable Convertible Preferred Stock Authorized Redeemable Convertible Preferred Stock Outstanding Liquidation Value Carrying Value Original Issue Price Per Share Temporary Equity Original Issue Price Per Share Number of common stock voting rights held per share. Common stock, voting rights Common Stock Voting Rights Number of common stock voting rights held per share Number Of Common Stock Voting Rights Held Per Share Common stock, dividends declared Dividends Common Stock Schedule Of Stock By Class [Table] Schedule Of Stock By Class [Table] Award Type Award Type [Axis] Award Type Share Based Compensation Arrangements By Share Based Payment Award Award Type And Plan Name [Domain] Exercise of outstanding options. Exercise of Outstanding Options Exercise Of Outstanding Options [Member] Issuance of Common Stock Options Employee Stock Option [Member] Plan Name Plan Name [Axis] Plan Name Plan Name [Domain] Two Thousand Fifteen And Nineteen Equity Incentive Plans Member. 2015 and 2019 Plans Two Thousand Fifteen And Nineteen Equity Incentive Plans [Member] Two thousand fifteen equity incentive plan. 2015 Plan Two Thousand Fifteen Equity Incentive Plan [Member] Two thousand nineteen incentive award plan. 2019 Plan Two Thousand Nineteen Incentive Award Plan [Member] Employee stock purchase plan. Employee Stock Purchase Plan Employee Stock Purchase Plan [Member] Conversion of Series A Redeemable Convertible Preferred Stock Conversion of Series B Redeemable Convertible Preferred Stock Class Of Stock [Line Items] Class Of Stock [Line Items] Number of common stock reserved for future issuance Common Stock Capital Shares Reserved For Future Issuance Percentage of voting power of all classes of stock. Schedule Of Share Based Compensation Arrangements By Share Based Payment Award [Table] Schedule Of Share Based Compensation Arrangements By Share Based Payment Award [Table] Incentive stock options and nonqualified stock options. Incentive Stock Options and Nonqualified Stock Options Incentive Stock Options And Nonqualified Stock Options [Member] Incentive stock options. Incentive Stock Options Incentive Stock Options [Member] 2019 Equity Incentive Plan Maximum [Member] Title of Individual Title Of Individual [Axis] Title of Individual Title Of Individual With Relationship To Entity [Domain] Ten percent stockholder. 10% Stockholder Ten Percent Stockholder [Member] Vesting Vesting [Axis] Vesting Vesting [Domain] Cliff Vesting Share Based Compensation Award Tranche One [Member] Balance Sheet Location Balance Sheet Location [Axis] Balance Sheet Location Balance Sheet Location [Domain] Other Current Liabilities and Other Non-Current Liabilities Other Liabilities [Member] Antidilutive Securities Antidilutive Securities Excluded From Computation Of Earnings Per Share By Antidilutive Securities [Axis] Antidilutive Securities, Name Antidilutive Securities Name [Domain] Non-employees. Non-employees Non Employees [Member] Restricted Stock Restricted Stock [Member] Share Based Compensation Arrangement By Share Based Payment Award [Line Items] Share Based Compensation Arrangement By Share Based Payment Award [Line Items] Percentage of exercise price of stock option on estimated fair value of shares Sharebased Compensation Arrangement By Sharebased Payment Award Purchase Price Of Common Stock Percent Percentage of exercise price of stock option granted to employee Percentage Of Voiting Power Term of options Sharebased Compensation Arrangement By Sharebased Payment Award Expiration Period Vesting period of options Share Based Compensation Arrangement By Share Based Payment Award Award Vesting Period1 Share Based Compensation [Abstract] Schedule Of Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Table] Schedule Of Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Table] Income Statement Location Income Statement Location [Axis] Income Statement Location Income Statement Location [Domain] Research and Development Research And Development Expense [Member] General and Administrative General And Administrative Expense [Member] Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items] Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items] Total stock-based compensation expense Allocated Share Based Compensation Expense Share-based compensation arrangement by Share-based payment award number of shares available for grant granted in period. Share-based compensation arrangement by share-based payment award, number of shares available for grant, exercised in period. Share-based Compensation arrangement by share-based payment award, number of shares available for grant, repurchased in period. Share-based compensation arrangement by share-based payment award, number of shares available for grant, cancelled in period. Outstanding Options, Shares available for Grant, Beginning balance Share Based Compensation Arrangement By Share Based Payment Award Number Of Shares Available For Grant Outstanding Options, Shares available for Grant, Additional shares authorized Share Based Compensation Arrangement By Share Based Payment Award Number Of Additional Shares Authorized Outstanding Options, Shares available for Grant, Options granted Share Based Compensation Arrangement By Share Based Payment Award Number Of Shares Available For Grant Granted In Period Outstanding Options, Shares available for Grant, Options exercised Share Based Compensation Arrangement By Share Based Payment Award Number Of Shares Available For Grant Exercised In Period Outstanding Options, Shares available for Grant, Options repurchased Share Based Compensation Arrangement By Share Based Payment Award Number Of Shares Available For Grant Repurchased In Period Outstanding Options, Shares available for Grant, Options canceled Share Based Compensation Arrangement By Share Based Payment Award Number Of Shares Available For Grant Cancelled In Period Outstanding Options, Shares available for Grant, Ending balance Share-based compensation arrangement by share-based payment award, options, additional shares authorized. Share-based compensation arrangement by share-based payment award, options, repurchased in period. Outstanding Options, Shares, Beginning balance Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Number Outstanding Options, Shares, Additional shares authorized Share Based Compensation Arrangement By Share Based Payment Award Options Additional Shares Authorized Outstanding Options, Shares, Options granted Share Based Compensation Arrangement By Share Based Payment Award Options Grants In Period Gross Outstanding Options, Shares, Options exercised Outstanding Options, Shares, Options repurchased Share Based Compensation Arrangement By Share Based Payment Award Options Repurchased In Period Outstanding Options, Shares, Options canceled Share Based Compensation Arrangement By Share Based Payment Award Options Forfeitures In Period Outstanding Options, Shares, Ending balance Outstanding Options, Shares, Exercisable Share Based Compensation Arrangement By Share Based Payment Award Options Exercisable Number Outstanding Options, Shares, Vested and expected to vest Share Based Compensation Arrangement By Share Based Payment Award Options Vested And Expected To Vest Outstanding Number Share-based compensation arrangements by share-based payment award, options, repurchased in period, weighted average exercise price. Outstanding Options, Weighted-Average Exercise Price, Beginning balance Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Weighted Average Exercise Price Outstanding Options, Weighted-Average Exercise Price, Options granted Share Based Compensation Arrangements By Share Based Payment Award Options Grants In Period Weighted Average Exercise Price Outstanding Options, Weighted-Average Exercise Price, Options exercised Share Based Compensation Arrangements By Share Based Payment Award Options Exercises In Period Weighted Average Exercise Price Outstanding Options, Weighted-Average Exercise Price, Options repurchased Share Based Compensation Arrangements By Share Based Payment Award Options Repurchased In Period Weighted Average Exercise Price Outstanding Options, Weighted-Average Exercise Price, Options canceled Share Based Compensation Arrangements By Share Based Payment Award Options Forfeitures In Period Weighted Average Exercise Price Outstanding Options, Weighted-Average Exercise Price, Ending balance Outstanding Options, Weighted-Average Exercise Price, Exercisable Share Based Compensation Arrangement By Share Based Payment Award Options Exercisable Weighted Average Exercise Price Outstanding Options, Weighted-Average Exercise Price, Vested and expected to vest Share Based Compensation Arrangement By Share Based Payment Award Options Vested And Expected To Vest Outstanding Weighted Average Exercise Price Outstanding Options, Weighted Average Remaining Contractual Term (Years) Sharebased Compensation Arrangement By Sharebased Payment Award Options Outstanding Weighted Average Remaining Contractual Term2 Outstanding Options, Weighted Average Remaining Contractual Term (Years), Exercisable Sharebased Compensation Arrangement By Sharebased Payment Award Options Exercisable Weighted Average Remaining Contractual Term1 Outstanding Options, Weighted Average Remaining Contractual Term (Years), Vested and expected to vest Sharebased Compensation Arrangement By Sharebased Payment Award Options Vested And Expected To Vest Exercisable Weighted Average Remaining Contractual Term1 Weighted-average grant-date fair value of options granted Share Based Compensation Arrangement By Share Based Payment Award Options Grants In Period Weighted Average Grant Date Fair Value Aggregate intrinsic value of options exercised Share Based Compensation Arrangement By Share Based Payment Award Options Exercises In Period Total Intrinsic Value Total unrecognized stock-based compensation expense for stock options Employee Service Share Based Compensation Nonvested Awards Total Compensation Cost Not Yet Recognized Stock Options Total unrecognized stock-based compensation expense, weighted-average period of recognition Employee Service Share Based Compensation Nonvested Awards Total Compensation Cost Not Yet Recognized Period For Recognition1 Total fair value of options vested Sharebased Compensation Arrangement By Sharebased Payment Award Options Vested In Period Fair Value1 Number of shares of common stock subject to repurchase at a period end. Amount of aggregate exercise price of early exercised shares of common stock at a period end. Common stock repurchased Shares subject to repurchase Shares Common Stock Subject To Repurchase Aggregate exercise prices of early exercised shares Aggregate Exercise Price Of Early Exercised Shares Common Stock Stock options granted to purchase shares Expected term Sharebased Compensation Arrangement By Sharebased Payment Award Fair Value Assumptions Expected Term1 Expected volatility Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Expected Volatility Rate Expected volatility, minimum Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Expected Volatility Rate Minimum Expected volatility, maximum Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Expected Volatility Rate Maximum Risk-free interest rate Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Risk Free Interest Rate Risk-free interest rate, minimum Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Risk Free Interest Rate Minimum Risk-free interest rate, maximum Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Risk Free Interest Rate Maximum Dividend yield Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Expected Dividend Rate Estimated dividend yield Number of Shares Underlying Outstanding Restricted Stock Awards, Unvested, December 31, 2018 Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nonvested Number Number of Shares Underlying Outstanding Restricted Stock Awards, Vested Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Vested In Period Number of Shares Underlying Outstanding Restricted Stock Awards, Unvested, September 30, 2019 Weighted Average Grant Date Fair Value, Unvested, December 31, 2018 Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nonvested Weighted Average Grant Date Fair Value Weighted Average Grant Date Fair Value, Vested Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Vested In Period Weighted Average Grant Date Fair Value Weighted Average Grant Date Fair Value, Unvested, September 30, 2019 Aggregate purchase price of unvested restricted stock at a period end. Founder shares issued under restricted stock agreements Stock Issued During Period Shares Restricted Stock Award Gross Stock-based compensation expense Total fair value of stock vested Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Vested In Period Total Fair Value Aggregate purchase price of unvested restricted stock subject to repurchase Aggregate Purchase Price Of Unvested Restricted Stock Subject To Repurchase Weighted average number of shares issued basic and diluted. Numerator: Net Income Loss [Abstract] Denominator: Weighted Average Number Of Shares Outstanding [Abstract] Weighted-average shares outstanding Weighted Average Number Of Shares Issued Basic And Diluted Less: weighted-average unvested restricted shares and shares subject to repurchase Weighted Average Number Of Shares Common Stock Subject To Repurchase Or Cancellation Schedule Of Antidilutive Securities Excluded From Computation Of Earnings Per Share [Table] Schedule Of Antidilutive Securities Excluded From Computation Of Earnings Per Share [Table] Unvested restricted stock awards. Unvested Restricted Stock Awards Unvested Restricted Stock Awards [Member] Unvested early exercised common stock options. Unvested Early Exercised Common Stock Options Unvested Early Exercised Common Stock Options [Member] Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items] Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items] Potentially dilutive securities Antidilutive Securities Excluded From Computation Of Earnings Per Share Amount Schedule Of Related Party Transactions By Related Party [Table] Schedule Of Related Party Transactions By Related Party [Table] Related Party Related Party Transactions By Related Party [Axis] Related Party Related Party [Domain] Former director. Former Director Former Director [Member] Related Party Transaction [Line Items] Related Party Transaction [Line Items] Expenses in relation to agreements with related parties Related Party Transaction Expenses From Transactions With Related Party Accounts payable Due To Related Parties Current