Entity Central Index Key Document And Entity Information [Abstract] Document And Entity Information [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 Current Fiscal Year End Date Current Fiscal Year End Date Entity Filer Category Entity Filer Category Entity Shell Company Entity Shell Company Entity Small Business Entity Small Business 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 Entity File Number Entity File Number Entity Tax Identification Number Entity Tax Identification Number Entity Address, Address Line One Entity Address Address Line1 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 Statement Of Financial Position [Abstract] Assets Assets [Abstract] Current assets: Assets Current [Abstract] Cash and cash equivalents Cash And Cash Equivalents At Carrying Value 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 Operating lease right-of-use asset Operating Lease Right Of Use Asset Other assets Other Assets Noncurrent Total assets Assets Liabilities and stockholders’ equity Liabilities And Stockholders Equity [Abstract] Current liabilities: Liabilities Current [Abstract] Accounts payable Accounts Payable Current Accrued and other current liabilities Accrued Liabilities Current Operating lease liability Operating Lease Liability Current Total current liabilities Liabilities Current Operating lease liability, net of current portion Operating Lease Liability Noncurrent Other liabilities Other Liabilities Noncurrent Total liabilities Liabilities Commitments and contingencies (Note 6) Commitments And Contingencies Stockholders’ equity: Stockholders Equity [Abstract] Common stock, $0.0001 par value, 490,000,000 shares authorized at June 30, 2019 and December 31, 2018; 36,931,141 and 36,829,857 shares issued and outstanding at June 30, 2019 and December 31, 2018, respectively Common Stock Value Additional paid-in capital Additional Paid In Capital Common Stock Accumulated other comprehensive loss Accumulated Other Comprehensive Income Loss Net Of Tax Accumulated deficit Retained Earnings Accumulated Deficit Total stockholders’ equity Stockholders Equity Total liabilities and stockholders’ equity Liabilities And Stockholders Equity 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 Interest expense (includes $1,005 and $1,867 attributable to related parties for the three and six months ended June 30, 2018, respectively) Interest Expense Other income (expense), net (includes $191 and $1,585 other expense attributable to related parties for the three and six months ended June 30, 2018, respectively) Other Nonoperating Income Expense Net loss Net Income Loss Net loss per common share, basic and diluted Earnings Per Share Basic And Diluted Weighted-average common shares outstanding used in computing net loss per common share, basic and diluted Weighted Average Number Of Share Outstanding Basic And Diluted Other comprehensive income Other Comprehensive Income Loss Net Of Tax Portion Attributable To Parent [Abstract] Change in unrealized gains related to available-for-sale debt securities, net of tax Other Comprehensive Income Availableforsale Securities Adjustment Net Of Tax Portion Attributable To Parent Total other comprehensive income Other Comprehensive Income Loss Net Of Tax Portion Attributable To Parent Comprehensive loss Comprehensive Income Net Of Tax Interest expense attributable to related parties Interest Expense Related Party Other expense attributable to related parties Related Party Transaction Expenses From Transactions With Related Party Statement Of Stockholders Equity [Abstract] Statement [Table] Statement [Table] 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] Class of Stock Statement Class Of Stock [Axis] Class of Stock Class Of Stock [Domain] Redeemable Convertible Preferred Stock Redeemable Convertible Preferred Stock [Member] Statement [Line Items] Statement [Line Items] Beginning Balance Redeemable convertible preferred stock, shares outstanding, beginning balance Temporary Equity Shares Outstanding Redeemable convertible preferred stock, beginning balance Temporary Equity Carrying Amount Attributable To Parent Beginning balance, shares Shares Outstanding 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 Issuance of restricted stock awards Stock Issued During Period Value Restricted Stock Award Net Of Forfeitures Issuance of restricted stock awards, shares Stock Issued During Period Shares Restricted Stock Award Net Of Forfeitures Stock-based compensation expense Adjustments To Additional Paid In Capital Sharebased Compensation Requisite Service Period Recognition Value Net loss Ending Balance Redeemable convertible preferred stock, shares outstanding, ending balance Redeemable convertible preferred stock, ending balance Ending balance, shares Change in fair value of redeemable convertible preferred stock warrant liability. Change in fair value of embedded derivative liability. Increase decrease in operating lease right of use asset. Increase decrease in operating lease liability. Issuance of embedded derivative in connection to convertible notes. Unpaid offering costs. Statement Of Cash Flows [Abstract] Cash flows from operating activities Net Cash Provided By Used In Operating Activities [Abstract] 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 Depreciation Non-cash interest expense and amortization of debt discount and issuance cost Amortization Of Financing Costs And Discounts Change in fair value of redeemable convertible preferred stock warrant liability Change In Fair Value Of Redeemable Convertible Preferred Stock Warrant Liability Change in fair value of derivative instrument Change In Fair Value Of Embedded Derivative Liability Stock-based compensation Share Based Compensation Accretion of discount on available-for-sale securities Accretion Amortization Of Discounts And Premiums Investments Changes in assets and liabilities: Increase Decrease In Operating Capital [Abstract] Prepaid expenses and other current assets Increase Decrease In Prepaid Deferred Expense And Other Assets Operating lease right-of-use asset Increase Decrease In Operating Lease Right Of Use Asset Other assets Increase Decrease In Other Operating Assets Accounts payable Increase Decrease In Accounts Payable Accrued and other current liabilities Increase Decrease In Accrued Liabilities And Other Operating Liabilities Operating lease liability Increase Decrease In Operating Lease Liability Other liabilities Increase Decrease In Other Operating 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] Purchase of property and equipment Payments To Acquire Property Plant And Equipment Purchase of available-for-sale securities Payments To Acquire Available For Sale Securities Debt Proceeds from maturities of available-for-sale securities Proceeds From Maturities Prepayments And Calls Of Available For Sale 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 convertible notes (includes $9,560 from related parties for the six months ended June 30, 2018) Proceeds From Notes Payable Deferred offering costs Payments Of Stock Issuance Costs Debt issuance cost Payments Of Debt Issuance Costs Proceeds from issuance of common stock Proceeds From Issuance Of Common Stock Principal payments of capital lease Repayments Of Debt And Capital Lease Obligations Principal payments of tenant improvement allowance payable Payments For Tenant Improvements Net cash provided by financing activities Net Cash Provided By Used In Financing Activities Net increase (decrease) in cash, cash equivalents and restricted cash Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents Period Increase Decrease Excluding Exchange Rate Effect Cash, cash equivalents and restricted cash, at beginning of period Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents Including Disposal Group And Discontinued Operations Cash, cash equivalents and restricted cash, at end of period Reconciliation of cash, cash equivalents and restricted cash to statement of financial position Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents [Abstract] Supplemental disclosures of non-cash investing and financing information: Cash Flow Noncash Investing And Financing Activities Disclosure [Abstract] Purchase of property and equipment under accounts payable Noncash Or Part Noncash Acquisition Fixed Assets Acquired1 Issuance of derivative instrument related to convertible notes payable Issuance Of Embedded Derivative Unpaid offering costs Unpaid Offering Costs Deferred offering costs paid in restricted stock awards Debt Issuance Costs Incurred During Noncash Or Partial Noncash Transaction The cash inflow from issuance of convertible notes to related parties. Proceeds from issuance of convertible notes Proceeds From Issuance Of Convertible Notes To Related Parties Organization Consolidation And Presentation Of Financial Statements [Abstract] The Company Organization Consolidation And Presentation Of Financial Statements Disclosure [Text Block] Accounting Policies [Abstract] Summary of Significant Accounting Policies Significant Accounting Policies [Text Block] Accounts Payable And Accrued Liabilities Current [Abstract] Accrued and Other Current Liabilities Accounts Payable Accrued Liabilities And Other Liabilities Disclosure Current [Text Block] Fair Value Disclosures [Abstract] Fair Value Measurements Fair Value Disclosures [Text Block] Investments Debt And Equity Securities [Abstract] Marketable Securities Investments In Debt And Marketable Equity Securities And Certain Trading Assets Disclosure [Text Block] Commitments And Contingencies Disclosure [Abstract] Commitments and Contingencies Commitments And Contingencies 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] Basis of Presentation Basis Of Accounting Policy Policy [Text Block] Use of Estimates Use Of Estimates Leases Lessee Leases Policy [Text Block] Marketable Securities Marketable Securities Policy Recent Accounting Pronouncements New Accounting Pronouncements Policy Policy [Text Block] Schedule of accrued and other current liabilities. Schedule of Accrued and Other Current Liabilities Schedule Of Accrued And Other Current Liabilities Table [Text Block] Summary of Fair Value Hierarchy for Assets Measured at Fair Value on Recurring Basis Fair Value Assets Measured On Recurring Basis [Text Block] Summary of Marketable Securities Held Marketable Securities [Text Block] Summary of Future Payments Under Non-Cancelable Operating Lease Contractual Obligation Fiscal Year Maturity Schedule Table [Text Block] Summary of Stock Options Activity under 2018 Plan and 2015 Equity Incentive Plan Schedule Of Share Based Compensation Stock Options Activity Table [Text Block] Summary of Stock-based Compensation Classified in Condensed Consolidated Statements of Operations and Comprehensive Loss Schedule Of Compensation Cost For Share Based Payment Arrangements Allocation Of Share Based Compensation Costs By Plan 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] Summary of Anti-dilutive Securities Excluded from Computation of Diluted Net Loss per Share Schedule Of Antidilutive Securities Excluded From Computation Of Earnings Per Share [Text Block] Cash and cash equivalents and 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] Adjustments for New Accounting Pronouncements Adjustments For New Accounting Pronouncements [Axis] Type of Adoption Type Of Adoption [Member] Accounting Standards Update 2016-02 Accounting Standards Update201602 [Member] Summary Of Significant Accounting Policies [Line Items] Summary Of Significant Accounting Policies [Line Items] Operating lease liability Operating Lease Liability Accrued research and development current. Accrued legal fees current. Accrued research and development Accrued Research And Development Current Accrued salaries and benefits Employee Related Liabilities Current Accrued legal fees Accrued Legal Fees Current Accrued professional fees Accrued Professional Fees Current Accrued other liabilities Other Accrued Liabilities Current Total accrued and other current liabilities Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Table] Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Table] Significant Observable Inputs (Level 2) Fair Value By Fair Value Hierarchy Level [Axis] Fair Value Hierarchy and NAV Fair Value Measurements Fair Value Hierarchy [Domain] Quoted Price in Active Markets (Level 1) Fair Value Inputs Level1 [Member] Significant Observable Inputs (Level 2) Fair Value Inputs Level2 [Member] Significant Unobservable Inputs (Level 3) Fair Value Inputs Level3 [Member] Measurement Frequency Fair Value By Measurement Frequency [Axis] Fair Value, Measurement Frequency Fair Value Measurement Frequency [Domain] Fair Value, Measurements, Recurring Fair Value Measurements Recurring [Member] Asset Class Fair Value By Asset Class [Axis] Asset Class Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation By Asset Class [Domain] Money Market Funds Money Market Funds [Member] Commercial Paper Commercial Paper [Member] Corporate Notes Corporate Note Securities [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] Cash equivalents Cash And Cash Equivalents Fair Value Disclosure Marketable securities Available For Sale Securities Debt Securities Total Assets Fair Value Disclosure Marketable Securities [Table] Marketable Securities [Table] Investment Type Investment Type [Axis] Investments Investment Type Categorization [Member] Marketable Securities [Line Items] Marketable Securities [Line Items] Amortized Cost Available For Sale Debt Securities Amortized Cost Basis Unrealized Gains Available For Sale Debt Securities Accumulated Gross Unrealized Gain Before Tax Unrealized Losses Available For Sale Debt Securities Accumulated Gross Unrealized Loss Before Tax Fair Value Range Range [Axis] Range Range [Member] Maximum Maximum [Member] Minimum Minimum [Member] Marketable securities, contractual maturities Debt Securities Available For Sale Term Realized gains or losses recognized on sale or maturity of available-for-sale debt securities Debt Securities Available For Sale Realized Gain Loss Impairment charges related to marketable securities Other Than Temporary Impairment Loss Debt Securities Available For Sale Estimated incremental borrowing rate used to determine discounted present value of remaining lease payments Operating Lease Weighted Average Discount Rate Percent Remaining operating lease term Operating Lease Weighted Average Remaining Lease Term1 Operating lease cost Operating Lease Cost Operating cash flows used for operating leases Operating Lease Payments Operating Lease Operating Lease Liabilities Payments Due [Abstract] 2019 (excluding the six months ended June 30, 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 Total undiscounted lease payments Lessee Operating Lease Liability Payments Due Less: imputed interest Lessee Operating Lease Liability Undiscounted Excess Amount Total operating lease liabilities Operating Lease Operating Leases Future Minimum Payments Due [Abstract] 2019 Operating Leases Future Minimum Payments Due Current 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 Total payments Operating Leases Future Minimum Payments Due Schedule Of Share Based Compensation Arrangements By Share Based Payment Award [Table] Schedule Of Share Based Compensation Arrangements By Share Based Payment Award [Table] Plan Name Plan Name [Axis] Plan Name Plan Name [Domain] Two thousand eighteen equity incentive plan. 2018 Equity Incentive Plan Two Thousand Eighteen Equity Incentive Plan [Member] Share Based Compensation Arrangement By Share Based Payment Award [Line Items] Share Based Compensation Arrangement By Share Based Payment Award [Line Items] Number of common stock available for issuance increased Share Based Compensation Arrangement By Share Based Payment Award Number Of Additional Shares Authorized Share-based compensation arrangement by share-based payment award, options, available for grant. Award Type Award Type [Axis] Equity Award Share Based Compensation Arrangements By Share Based Payment Award Award Type And Plan Name [Domain] Two thousand eighteen and two thousand fifteen equity incentive plan. 2018 Plan and 2015 Equity Incentive Plan Two Thousand Eighteen And Two Thousand Fifteen Equity Incentive Plan [Member] Number of Shares Available for Grant Share Based Compensation Arrangement By Share Based Payment Award Options Available For Grant Roll Forward Beginning balance Share Based Compensation Arrangement By Share Based Payment Award Number Of Shares Available For Grant Shares authorized Options granted Share Based Compensation Arrangement By Share Based Payment Award Options Grants In Period Gross Options forfeited or canceled Share Based Compensation Arrangement By Share Based Payment Award Options Forfeitures And Expirations In Period Ending balance Number of Shares Underlying Outstanding Options Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Roll Forward Beginning balance Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Number Options granted Options forfeited or canceled Options exercised Ending balance Weighted Average Exercise Price Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Weighted Average Exercise Price Rollforward Beginning balance Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Weighted Average Exercise Price Options granted Share Based Compensation Arrangements By Share Based Payment Award Options Grants In Period Weighted Average Exercise Price Options forfeited or canceled Share Based Compensation Arrangement By Share Based Payment Award Options Forfeitures And Expirations In Period Weighted Average Exercise Price Options exercised Share Based Compensation Arrangements By Share Based Payment Award Options Exercises In Period Weighted Average Exercise Price Ending balance Share-based compensation arrangement by share-based payment award, options, weighted average remaining contractual term. Weighted Average Remaining Contractual Term (in years) Share Based Compensation Arrangement By Share Based Payment Award Options Weighted Average Remaining Contractual Term [Abstract] Weighted Average Remaining Contractual Term (in years) Sharebased Compensation Arrangement By Sharebased Payment Award Options Outstanding Weighted Average Remaining Contractual Term2 Share-based compensation arrangement by share-based payment award, options, aggregate intrinsic value. Aggregate Intrinsic Value Share Based Compensation Arrangement By Share Based Payment Award Options Aggregate Intrinsic Value [Abstract] Beginning balance Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Intrinsic Value Options exercised Share Based Compensation Arrangement By Share Based Payment Award Options Exercises In Period Total Intrinsic Value Ending balance 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 Allocated Share Based Compensation Expense Unrecognized stock-based compensation of unvested employee options and unvested RSAs and RSUs Employee Service Share Based Compensation Nonvested Awards Total Compensation Cost Not Yet Recognized Unrecognized stock-based compensation of unvested stock awards, weighted-average period expected for recognition Employee Service Share Based Compensation Nonvested Awards Total Compensation Cost Not Yet Recognized Period For Recognition1 Weighted average number of shares outstanding adjustment. Earnings Per Share Basic And Diluted [Abstract] Numerator: Net Income Loss Available To Common Stockholders Basic [Abstract] Net loss attributable to common stockholders Denominator: Weighted Average Number Of Shares Outstanding [Abstract] Weighted-average common shares outstanding Weighted Average Number Of Shares Issued Basic Less: weighted-average unvested restricted shares and shares subject to repurchase Weighted Average Number Of Shares Outstanding Adjustment Net loss per share attributable to common stockholders, basic and diluted Schedule Of Antidilutive Securities Excluded From Computation Of Earnings Per Share [Table] Schedule Of Antidilutive Securities Excluded From Computation Of Earnings Per Share [Table] Antidilutive Securities Antidilutive Securities Excluded From Computation Of Earnings Per Share By Antidilutive Securities [Axis] Antidilutive Securities, Name Antidilutive Securities Name [Domain] Options to Purchase Common Stock Employee Stock Option [Member] 2017 convertible notes. 2017 Convertible Notes Two Thousand Seventeen Convertible Notes [Member] 2018 convertible notes. 2018 Convertible Notes Two Thousand Eighteen Convertible Notes [Member] Redeemable convertible preferred stock warrants. Redeemable Convertible Preferred Stock Warrants Redeemable Convertible Preferred Stock Warrants [Member] Unvested Restricted Stock Awards Restricted Stock [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] Anti-dilutive securities excluded from the computation of diluted net loss per share Antidilutive Securities Excluded From Computation Of Earnings Per Share Amount The 2018 convertible notes were automatically convertible into shares of the Company’s common stock at a price equal to 80% of the initial price to public in a qualified initial public offering if such offering was completed prior to February 2, 2019. 2017 Convertible Notes Sale of Stock Subsidiary Sale Of Stock [Axis] Sale of Stock Sale Of Stock Name Of Transaction [Domain] Initial Public Offering I P O [Member] Convertible notes, principal amount Debt Instrument Carrying Amount Convertible notes, accrued but unpaid interest Interest Payable Current And Noncurrent Convertible notes, conversion price per share of common stock Debt Instrument Convertible Conversion Price1 Convertible notes, conversion price per share of common stock Shares Issued Price Per Share Percentage of initial public offering per share price Percentage Of Initial Public Offering Per Share Price