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Lease, Square Footage Of Leased Space Lessee, Operating Lease, Square Footage Of Leased Space Preferred stock issued Temporary Equity, Stock Issued During Period, Value, New Issues Accumulated Deficit Retained Earnings [Member] Shares of restricted stock issued to founders (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period Collaborative arrangement, numerator for determining additional consideration Collaborative Arrangement, Numerator For Determining Additional Consideration Collaborative Arrangement, Numerator For Determining Additional Consideration Document Period End Date Document Period End Date Statement [Table] Statement [Table] Entity Registrant Name Entity Registrant Name Purchases of marketable securities Payments to Acquire Debt Securities, Available-for-sale Temporary Equity, by Class of Stock [Table] Temporary Equity, by Class of Stock [Table] Based number of options issuable (in shares) Share-based Compensation 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Agreement, Number Of Shares Issuable Vesting [Axis] Vesting [Axis] 2021 Lessee, Operating Lease, Liability, Payments, Due Year Two Subsidiary, Sale of Stock [Line Items] Subsidiary, Sale of Stock [Line Items] Other long-term liabilities Other Liabilities, Noncurrent City Area Code City Area Code Risk-free interest rate, minimum Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate, Minimum Stock Purchase Agreement, Tranche Three Stock Purchase Agreement, Tranche Three [Member] Stock Purchase Agreement, Tranche Three Prepaid expenses and other current assets Increase (Decrease) in Prepaid Expense and Other Assets Title of 12(b) Security Title of 12(b) Security Vesting of founder shares subject to repurchase Stock Issued During Period, Vesting Of Founder Shares Subject To Repurchase, Value Stock Issued During Period, Vesting Of Founder Shares Subject To Repurchase, Value Exercisable, Weighted-Average Exercise Price (in USD per 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Prepaid Insurance CASH FLOWS FROM OPERATING ACTIVITIES: Net Cash Provided by (Used in) Operating Activities [Abstract] Total operating expenses Operating Expenses AstraZeneca AstraZeneca [Member] AstraZeneca Number of shares held in VIE (in shares) Variable Interest Entities, Number Of Shares Held Variable Interest Entities, Number Of Shares Held Less: Amounts representing interest Lessee, Operating Lease, Liability, Undiscounted Excess Amount Issuance of common stock upon the exercise of stock options Stock Issued During Period, Value, Stock Options Exercised Net loss per share, basic and diluted (in USD per share) Earnings Per Share, Basic and Diluted Summary of Cash and Cash Equivalents Schedule of Cash and Cash Equivalents [Table Text Block] Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Income Statement Location [Domain] Income Statement Location [Domain] Statistical Measurement [Axis] Statistical Measurement 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Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate, Minimum Performance Condition Restricted Stock Performance Condition Restricted Stock [Member] Performance Condition Restricted Stock Variable lease cost Variable Lease, Cost Preferred stock issued (in shares) Temporary Equity, Stock Issued During Period, Shares, New Issues Temporary Equity, Stock Issued During Period, Shares, New Issues Emerging Growth Company Status Emerging Growth Company Status [Policy Text Block] Emerging Growth Company Status Common stock, shares authorized (in shares) Common Stock, Shares Authorized Statement of Cash Flows [Abstract] Entity Central Index Key Entity Central Index Key Convertible preferred stock, shares authorized (in shares) Temporary Equity, Shares Authorized Beginning balance (in shares) Ending balance (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number Entity Emerging 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Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested, Weighted Average Grant Date Fair Value Recognition period for unrecognized compensation costs related to unvested options expected to vest Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition Accounting Policies [Abstract] Liquidation Preference Temporary Equity, Liquidation Preference Additional Paid-In Capital Additional Paid-in Capital [Member] Stock-Based Compensation Share-based Payment Arrangement [Policy 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] Cash and Cash Equivalents [Line Items] Cash and Cash Equivalents [Line Items] Entity Address, Address Line One Entity Address, Address Line One Entity Address, Address Line Two Entity Address, Address Line Two Cash and cash equivalents and debt securities, 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activities Net Cash Provided by (Used in) Investing Activities Fair Value, Recurring and Nonrecurring [Table] Fair Value, Recurring and Nonrecurring [Table] Convertible Preferred Stock Stockholders' Equity Note, Redeemable Preferred Stock, Issue, Policy [Policy Text Block] Monthly basis Share-based Payment Arrangement, Tranche Two [Member] Lessee, Lease, Description [Table] Lessee, Lease, Description [Table] Cash, cash equivalents, and marketable securities Cash, Cash Equivalents, and Short-term Investments General and administrative General and Administrative Expense Accounts payable Accounts Payable, Current Accrued liabilities Total accrued liabilities Accrued Liabilities, Current Entity Interactive Data Current Entity Interactive Data Current Westlake Village, California Lease Arrangement Westlake Village, California Lease Arrangement [Member] Westlake Village, California Lease Arrangement Common stock, shares, issued (in shares) Common Stock, Shares, Issued Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Common stock, par value (in USD per share) Common Stock, Par or Stated Value Per Share Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Available letter of credit Lessee, Operating Lease, Letter Of Credit Requirement Lessee, Operating Lease, Letter Of Credit Requirement Beginning balance (in USD per share) Ending balance (in USD per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Net Loss Per Share Earnings Per Share [Text Block] Components of Shares of Stock for Issuance Schedule of Stock by Class [Table Text Block] Vesting of founder shares subject to repurchase (in shares) Stock Issued During Period, 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(in shares) Stock Issued During Period, Shares, New Issues Vesting Rights, Percentage Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage Restricted stock units outstanding RSU's subject to future vesting Restricted Stock Units (RSUs) [Member] Research and development Research and Development Expense [Member] Debt Securities, Available-for-sale [Table] Debt Securities, Available-for-sale [Table] 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] Lapse of repurchase rights related to common stock issued pursuant to early exercises (in shares) Stock Issued During Period, Lapse of Repurchase Rights Related to Common Stock Issued Pursuant to Early Exercises, Shares Stock Issued During Period, Lapse of Repurchase Rights Related to Common Stock Issued Pursuant to Early Exercises, Shares Total liabilities Liabilities Common stock, $0.0001 par value; 300,000,000 and 65,820,000 shares authorized at June 30, 2020 and December 31, 2019, respectively; 38,189,287 and 2,879,763 shares issued at June 30, 2020 and December 31, 2019, respectively; 37,690,058 and 2,120,853 shares outstanding at June 30, 2020 and December 31, 2019, respectively Common Stock, Value, Issued Proceeds from maturities of marketable securities Proceeds from Maturities, Prepayments and Calls of Debt Securities, Available-for-sale Research and development Research and Development Expense Early exercised options subject to future vesting Early Exercised Options [Member] Early Exercised Options Vesting [Domain] Vesting [Domain] Counterparty Name [Domain] Counterparty Name [Domain] Statement of Comprehensive Income [Abstract] Statement of Comprehensive Income [Abstract] Schedule of Cash and Cash Equivalents [Table] Schedule of Cash and Cash Equivalents [Table] Allowance for credit loss Debt Securities, Available-for-sale, Allowance for Credit Loss Expected volatility, maximum Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate, Maximum Cash and cash equivalents Cash and Cash Equivalents, at Carrying Value License Agreements Collaborative Arrangement Disclosure [Text Block] Operating lease right-of-use asset Operating Lease, Right-of-Use Asset Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract] Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract] Equity Components [Axis] Equity Components [Axis] Weighted-Average Grant Date Fair Value Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract] Cash and Cash Equivalents [Domain] Cash and Cash Equivalents [Domain] Total stockholders’ equity (deficit) Beginning Balance Ending Balance Stockholders' Equity Attributable to Parent Forfeited (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period Grant date fair value of options vested during the period Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested in Period, Fair Value Net amortization/accretion on marketable securities Accretion (Amortization) of Discounts and Premiums, Investments Convertible Debt Convertible Debt [Member] Fair Value Measurements Fair Value Disclosures [Text Block] Tenant improvement allowance Less: Tenant improvement allowance Lessee, Operating Lease, Tenant Improvement Allowance Lessee, Operating Lease, Tenant Improvement Allowance Operating Lease Supplemental Cash Flow Information Lease, Cost [Table Text Block] Conversion of preferred stock into common stock upon initial public offering Stock Issued During Period, Value, Conversion of Convertible Securities Preferred stock, $0.0001 par value; 10,000,000 and no shares authorized at June 30, 2020 and December 31, 2019, respectively; no shares issued and outstanding at June 30, 2020 and December 31, 2019; Preferred Stock, Value, Issued Convertible preferred stock, shares outstanding (in shares) Beginning balance, convertible preferred stock (in shares) Ending balance, convertible preferred stock (in shares) Temporary Equity, Shares Outstanding Cash and cash equivalents Cash and cash equivalents, estimated fair value Cash and Cash Equivalents, Fair Value Disclosure Security Exchange Name Security Exchange Name Potentially antidilutive shares excluded from the calculation of net loss per share Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Depreciation Depreciation Long-term Debt, Type [Axis] Long-term Debt, Type [Axis] Marketable securities Debt Securities, Available-for-sale, Current Net cash used in operating activities Net Cash Provided by (Used in) Operating Activities Number of Units Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] Equity Component [Domain] Equity Component [Domain] Votes per share of common stock Common Stock, Voting Rights, Number Of Votes Per Share Common Stock, Voting Rights, Number Of Votes Per Share Expected term (in years) Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term Document Transition Report Document Transition Report Stock Options Stock options to purchase common stock Share-based Payment Arrangement, Option [Member] Employee Stock Purchase Plan ESPP shares subject to future issuance Employee Stock [Member] U.S. government securities US Government Corporations and Agencies Securities [Member]