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Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table Text Block] Anti-dilutive Securities Excluded from Calculation of Diluted Net Loss Per Share Common Stock Valuation Stockholders' Equity, Policy [Policy Text Block] Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items] Fair Value Measurement Inputs and Valuation Techniques [Line Items] Entity Address, Postal Zip Code Entity Address, Postal Zip Code Document Fiscal Period Focus Document Fiscal Period Focus Reconciliation of Cash, Cash Equivalents and Restricted Cash Restrictions on Cash and Cash Equivalents [Table Text Block] Deferred offering costs Deferred Offering Costs Valuation allowance Valuation allowance Deferred tax assets, valuation allowance Deferred Tax Assets, Valuation Allowance Deferred Tax Assets, Valuation Allowance, Total Preferred stock, $0.0001 par value; 80,000,000 shares authorized at December 31, 2022 and 2021; no shares issued and outstanding at December 31, 2022 and 2021 Preferred Stock, Value, Issued, Ending Balance Preferred Stock, Value, Issued, Beginning Balance Preferred Stock, Value, Issued, Total Preferred Stock, Value, Issued Stock-based compensation expense APIC, Share-Based Payment Arrangement, Increase for Cost Recognition APIC, Share-based Payment Arrangement, Increase for Cost Recognition, Total Deferred tax liabilities: Deferred Tax Liabilities, Gross [Abstract] Reimbursement of certain initial manufacturing costs Reimbursement Of Certain Initial Manufacturing Costs Reimbursement of certain initial manufacturing costs. 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California CALIFORNIA Statement of Financial Position [Abstract] Conversion of preferred stock to common stock upon initial public offering Conversion of Stock, Amount Issued Convertible preferred stock, shares issued Preferred shares issued Temporary equity, shares issued Change in fair value of purchase right liability Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings Securities Act File Number Entity File Number Stock issued during period in connection with licensing agreement shares. Stock Issued During Period in Connection with Licensing Agreement Shares Issuance of common stock in connection with license agreement, shares Scenario Scenario [Domain] NiKang Therapeutics, Inc. Ni Kang Therapeutics Incorporation [Member] NiKang Therapeutics, Inc. Statement of Cash Flows [Abstract] Thereafter Lessee, Operating Lease, Liability, to be Paid, after Year Five Valuation Approach and Technique [Domain] Issuance of common stock to Erasca Foundation Issuance of common stock to Erasca Foundation Issuance of common stock to foundation. Issuance of common stock to Erasca Foundation Issuance Of Common Stock To Foundation Retirement Plan Retirement Benefits [Text Block] Geographical Geographical [Domain] Statistical Measurement Statistical Measurement [Domain] Charitable Contribution Carryforward Expiration Year Charitable contribution carryforward expiration year Charitable contribution carryforward expiration year. 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Classification and Accretion of Convertible Preferred Stock Stockholders' Equity Note, Redeemable Preferred Stock, Issue, Policy [Policy Text Block] Other Effective Income Tax Rate Reconciliation, Other Adjustments, Percent Assets: Assets, Fair Value Disclosure [Abstract] Fair Value Hierarchy and NAV Fair Value Hierarchy and NAV [Axis] License Agreements [Table] License Agreements [Table] License agreements. Share-based Compensation Share-Based Payment Arrangement [Policy Text Block] Auditor Name Equity [Abstract] Accrued research and development expenses Accrued Research and Development Expenses Current Accrued research and development expenses current. Weighted-average exercise price, Canceled Share-Based Compensation Arrangements by Share-Based Payment Award, Options, Forfeitures in Period, Weighted Average Exercise Price Loss from operations Operating Income (Loss) Lessee, Operating Lease, Option to Extend Operating lease option to extend California California Franchise Tax Board [Member] Related Party [Domain] Additional Paid in Capital, Common Stock, Beginning Balance Additional Paid in Capital, Common Stock, Ending Balance Additional paid-in capital Additional Paid in Capital, Common Stock Convertible preferred stock (Series A, B-1 and B-2), $0.0001 par value; no shares and 97,622,409 shares authorized as of December 31, 2021 and 2020, respectively; no shares and 69,584,682 shares issued and outstanding as of December 31, 2021 and 2020, respectively; aggregate liquidation preference of $0 and $230,924 as of December 31, 2021 and 2020, respectively Carrying value Convertible preferred stock, beginning balance, value Convertible preferred stock,ending balance, value Temporary Equity, Carrying Amount, Attributable to Parent Scenario Scenario [Axis] In-process research and development Research and Development in Process In-process research and development expenses Accrued Professional Fees, Current Accrued professional services Total Accrued expenses and other current liabilities Accrued Liabilities and Other Liabilities Fair value, Total Debt Securities, Available-for-Sale, Unrealized Loss Position Available for sale securities, gross unrealized loss position Common stock, voting rights Common Stock, Voting Rights Entity Filer Category Entity Filer Category Purchases of marketable securities Payments to Acquire Marketable Securities Maturities of marketable securities Proceeds from Sale and Maturity of Marketable Securities US Treasury Securities US Treasury Securities Short Term [Member] US treasury securities short term. 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Accumulated Other Comprehensive Income (Loss) AOCI Attributable to Parent [Member] Short-Term Investments [Member] Short-Term Investments Credit percentage on qualified wages on employment taxes Credit percentage on qualified wages on employment taxes Maturity Debt Securities, Available-for-Sale, Term Asset Class Asset Class [Axis] Documents Incorporated by Reference [Text Block] Entity Tax Identification Number Entity Tax Identification Number Income Statement Location Income Statement Location [Axis] Number of restricted stock shares outstanding, Forfeited Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Forfeited in Period Common stock, $0.0001 par value; 800,000,000 shares authorized at December 31, 2022 and 2021; 150,448,363 and 121,382,547 shares issued at December 31, 2022 and 2021, respectively; 149,333,258 and 119,102,505 shares outstanding at December 31, 2022 and 2021, respectively Common Stock, Value, Issued Common Stock, Value, Issued, Total Common Stock, Value, Issued, Beginning Balance Common Stock, Value, Issued, Ending Balance Retained Earnings (Accumulated Deficit), Total Accumulated deficit Retained Earnings (Accumulated Deficit) Retained Earnings (Accumulated Deficit), Beginning Balance Retained Earnings (Accumulated Deficit), Ending Balance Gain on remeasurement of Operating Lease Assets and Liabilities. 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License Agreements Disclosure Text Block License Agreements Stock Issued During Period, Shares, Restricted Stock Award, Net of Forfeitures Shares issued Stock Issued During Period, Shares, Restricted Stock Award, Net of Forfeitures, Total Price per share Sale of Stock, Price Per Share Shares issue, price per share Commitments and Contingencies Commitments and Contingencies Disclosure [Text Block] Weighted-average exercise price, Exercised Share-Based Compensation Arrangements by Share-Based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price Accumulated other comprehensive loss Accumulated Other Comprehensive Income (Loss), Net of Tax, Total Accumulated Other Comprehensive Income (Loss), Net of Tax Marketable securities and investments Marketable Securities, Policy [Policy Text Block] Entity Common Stock, Shares Outstanding Net loss Net loss Net Income (Loss) Attributable to Parent Valuation Technique, Option Pricing Model [Member] Black-Scholes Option Pricing Model Conversion of Preferred Stock in Future Issuance (B-2) Conversion of B2 preferred stock in future issuance. Conversion Of B2 Preferred Stock In Future Issuance [Member] Increase (decrease) related to prior year positions Unrecognized Tax Benefits Increases (Decrease) Resulting From Prior Period Tax Positions Unrecognized tax benefits increases (decrease) resulting from prior period tax positions Available of sale securities, unrealized loss position, Number of positions Debt Securities, Available-for-Sale, Unrealized Loss Position, Number of Positions Stock holding period for ownership change Stock Holding Period For Ownership Change Stock holding period for ownership change. Operating lease liabilities Operating Lease, Liability, Current Affini T Therapeutics, Inc. Affini-T Therapeutics, Inc Member. Affini-T Therapeutics, Inc Member Additional Paid-in Capital Additional Paid-in Capital [Member] Collaborative Arrangement and Arrangement Other than Collaborative Collaborative Arrangement and Arrangement Other than Collaborative [Domain] Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Table] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table] US Treasury Securities US Treasury Securities Long Term [Member] US treasury securities long term. Line of credit facility, expiration date Line of Credit Facility, Expiration Date At the Time Option is Granted At Time Option Is Granted [Member] At the time option is granted. Net operating loss carryforwards Deferred Tax Assets, Operating Loss Carryforwards Deferred Tax Assets, Operating Loss Carryforwards, Total Entity Registrant Name Entity Registrant Name Liabilities, Fair Value Disclosure, Total Total fair value of liabilities Liabilities, Fair Value Disclosure Cash and cash equivalents Cash and Cash Equivalents, at Carrying Value Cash and Cash Equivalents, at Carrying Value, Total Cash and Cash Equivalents, at Carrying Value, Beginning Balance Cash and Cash Equivalents, at Carrying Value, Ending Balance Net Loss Per Share Earnings Per Share [Text Block] Schedule of Share-Based Payment Award, Stock Options, Valuation Assumptions [Table Text Block] Assumptions used to Determine Fair Value of Stock Option Grants and Stock to be Purchased under ESPP Percentage of commission on gross sales proceeds Percentage Of Commission On Gross Sales Proceeds Percentage of commission on gross sales proceeds Class of Stock Class of Stock [Axis] US Government Agency Securities US Government Agencies Debt Securities [Member] Lessee Lease Description [Table] Lessee, Lease, Description [Table] Amounts accrued for purchases of property and equipment Amounts Accrued For Purchase Of Property And Equipment Amounts accrued for purchase of property and equipment. Stock-based compensation expense Share-Based Payment Arrangement, Noncash Expense Share-based Payment Arrangement, Noncash Expense, Total Shares of common stock subject to repurchase Shares Of Common Stock Subject To Repurchase Shares of common stock subject to repurchase. Issuance of common stock in connection with license agreement Issuance Of Common Stock In Connection With License Agreement Issuance of common stock in connection with license agreement. Property and equipment, net Property and equipment, net Property, Plant and Equipment, Net Property, Plant and Equipment, Net, Beginning Balance Property, Plant and Equipment, Net, Ending Balance Amounts accrued for offering costs Amounts accrued for offering costs Award Type Award Type [Domain] Statement [Line Items] Statement [Line Items] Liabilities: Liabilities, Fair Value Disclosure [Abstract] Title of 12(b) Security Title of 12(b) Security Accounts payable Increase (Decrease) in Accounts Payable Increase (Decrease) in Accounts Payable, Total Common Stock Common Stock [Member] Operating leases Noncancelable expiration dates Operating Leases Non Cancelable Expiration Dates Operating leases Noncancelable expiration dates. Other state. Other State [Member] Other State Share-based compensation, plan expiration period Share-Based Compensation Arrangement by Share-Based Payment Award, Expiration Period Cash and Cash Equivalents, Restricted Cash and Cash Equivalents, Policy [Policy Text Block] Cash, Cash Equivalents, and Restricted Cash Cash flows from operating activities: Net Cash Provided by (Used in) Operating Activities [Abstract] Equity Component Equity Component [Domain] Fair Value Measurements Fair Value Measurement, Policy [Policy Text Block] Convertible Preferred Stock Issued Convertible Preferred Stock Convertible Preferred Stock [Member] Fair Value, Liability, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] Share-based compensation, shares subject to repurchase Share Based Compensation Arrangement By Share Based Payment Award Shares Subject To Repurchase Share-based compensation arrangement by share-based payment award, shares subject to repurchase. Entity Address, State or Province Entity Address, State or Province 2026 Lessee, Operating Lease, Liability, to be Paid, Year Four Geographical Geographical [Axis] Net (decrease) increase in cash, cash equivalents and restricted cash Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect Document Type Document Type Summary Of Significant Accounting Policies [Table] Summary Of Significant Accounting Policies [Table] Summary of significant accounting policies. Payment for US patent application Payment Related To Publication Of U S Patent Application Payment related to publication of US patent application. US Government Agency Securities US Government Corporations and Agencies Securities [Member] Series B-1 Convertible Preferred Stock Series B1 Convertible Preferred Stock [Member] Series B-1 convertible preferred stock. Entity Shell Company Entity Shell Company Employee Stock Purchase Plan [Member] Employee stock purchase plan. ESPP Stock-based compensation Share-Based Payment Arrangement, Expense 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] Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Table] Fair Value, Recurring and Nonrecurring [Table] Security Exchange Name Security Exchange Name Corporate Debt Securities CorporateDebtSecuritiesShortTerm[Member] Corporate debt securities short term member Class of Stock [Line Items] Class of Stock [Line Items] Milestones accrued Milestones Accrued Milestones accrued. Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items] Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Summary of Significant Accounting Policies Significant Accounting Policies [Text Block] Net cash used in operating activities Net Cash Provided by (Used in) Operating Activities Unrecognized compensation cost expected to be recognized as expense, period Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term Weighted-average remaining contractual term (years), Outstanding For holders of more than 10% of the Company’s combined voting power of all classes of stock. For Holders of More Than 10% of Company's Total Combined Voting Power of All Classes of Stock For Holders Of More Than Ten Percent Of Combined Voting Power Of All Classes Of Stock [Member] Asset Acquisitions [Table] Asset Acquisitions [Table] Asset acquisitions. Commitments and Contingencies Disclosure [Abstract] Investment in equity securities Equity Securities without Readily Determinable Fair Value, Amount Expected Term (in years) Measurement Input, Expected Term [Member] Operating lease cost Operating Lease, Cost Schedule of Future Minimum Lease Payments under Operating Leases Lessee, Operating Lease, Liability, Maturity [Table Text Block] Reconciliation of Beginning and Ending Amount of Unrecognized Tax Benefits Schedule of Unrecognized Tax Benefits Roll Forward [Table Text Block] Change in valuation allowance Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Percent Share-Based Payment Arrangement, Restricted Stock Unit, Activity [Table Text Block] Summary of Restricted Stock Activity Summary of Stock Option Activity Share-Based Payment Arrangement, Option, Activity [Table Text Block] Recently Adopted Accounting Pronouncements and Recently Issued Accounting Pronouncements Not Yet Adopted New Accounting Pronouncements, Policy [Policy Text Block] Common stock, shares outstanding Beginning balance, shares Ending balance, shares Common Stock, Shares, Outstanding Jefferies LLC Jefferies LLC [Member] Jefferies LLC Member (Accretion) amortization on marketable securities, net Accretion (Amortization) of Discounts and Premiums, Investments Underwriters Option to Purchase Shares Over-Allotment Option [Member] Underwriters Option to Purchase Additional Shares Effective Income Tax Rate Reconciliation, Tax Credit, Research, Percent Research and Development credits Fair Value, Inputs, Level 2 [Member] Significant Other Observable Inputs (Level 2) Available for sale securities, Estimated fair value Debt Securities, Available-for-Sale Debt Securities, Available-for-sale, Total Cash flows from investing activities: Net Cash Provided by (Used in) Investing Activities [Abstract] Series B Agreement Series B Convertible Preferred Stock Purchase Agreement [Member] Series B convertible preferred stock purchase agreement. Increase related to current year positions Unrecognized Tax Benefits, Increase Resulting from Current Period Tax Positions Commitments and contingencies (Note 12) Commitments and Contingencies Temporary equity stock issued during period shares acquisition. Temporary Equity Stock Issued During Period Shares Acquisition Issuance of Series B-2 convertible preferred stock in connection with asset acquisition, Shares Income Tax Authority, Name [Domain] Ending balance, shares Beginning balance, shares Beginning balance, shares Common Stock, Shares, Issued, Total Common Stock, Shares, Issued Shares issued and sold Common stock, shares issued US Treasury Securities US Treasury Securities [Member] Recovery of stockholder's short-swing profits Disgorgement of Short-Swing Profits Disgorgement of short-swing profits. Minimum Minimum [Member] Income Tax Authority, Name [Axis] Awards Available for Future Grant Awards Available For Future Grant [Member] Awards available for future grant. Minimum stock holding percentage for ownership change Minimum Stock Holding Percentage For Ownership Change Minimum stock holding percentage for ownership change. Debt Securities, Available-for-Sale, Continuous Unrealized Loss Position, 12 Months or Longer, Number of Positions Available of sale securities, unrealized loss position, greater than 12 months, Number of positions Change in fair value of preferred stock purchase right liability Change In Fair Value Of Preferred Stock Purchase Right Liability Change in fair value of preferred stock purchase right liability. Change in fair value of preferred stock purchase right liability Risk-free interest rate, maximum Share-Based Compensation Arrangement by Share-Based Payment Award, Fair Value Assumptions, Risk Free Interest Rate, Maximum Unaudited Interim Financial Information Unaudited Interim Financial Information [Policy Text Block] Unaudited interim financial information. Lessee, Leases [Policy Text Block] Leases Weighted-average exercise price, Options exercisable at December 31, 2022 Weighted-average exercise price, Options exercisable at June 30, 2021 Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Exercisable, Weighted Average Exercise Price Accounting Standards Update Accounting Standards Update [Axis] Charitable contribution carryforward amount. Charitable Contribution Carryforward Amount Charitable contribution carryforward amount Tax Credit Carryforward [Axis] Stockholders' equity: Stockholders' Equity Attributable to Parent [Abstract] State income taxes, net of federal benefit Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Percent Effective income tax rate reconciliation state net operating loss. Effective Income Tax Rate Reconciliation State Net Operating Loss State net operating loss Long-term investments. Long-Term Investments [Member] Long-Term Investments Counterparty Name Counterparty Name [Axis] Entity Address, Address Line Two Entity Address, Address Line Two Weighted-average grant date fair value, Forfeited Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value Award Type Award Type [Axis] First Licensed Product First Licensed Product [Member] First licensed product. Subsequent Event Subsequent Event [Member] Purchase period Share-based Compensation Arrangement by Share-based Payment Award Purchase Period Share-based compensation arrangement by share-based payment award purchase period. Related Party Transaction [Domain] Total deferred tax assets Deferred Tax Assets, Gross Impairment of Long-Lived Assets Impairment or Disposal of Long-Lived Assets, Policy [Policy Text Block] Aggregate intrinsic value, Exercised Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Exercises in Period, Intrinsic Value Intrinsic value of options exercised Other (expense) income, net Other Nonoperating Income (Expense), Total Other Nonoperating Income (Expense) Increase to preferred stock purchase right liability for new issuances. Increase To Preferred Stock Purchase Right Liability For New Issuances Preferred stock purchase right liability Other income (expense) Nonoperating Income (Expense) [Abstract] Operating lease, aggregate monthly payments to lessor Total lease payments Lessee, Operating Lease, Liability, to be Paid Lease initial term Lessee, Operating Lease, Term of Contract Operating lease initial term Expected dividend yield Share-Based Compensation Arrangement by Share-Based Payment Award, Fair Value Assumptions, Expected Dividend Payments Proceeds from the disgorgement of stockholder's short-swing profits Proceeds From The Disgorgement Of Stockholder's Short-Swing Profits Proceeds from the disgorgement of stockholder's short-swing profits. Equity Securities FV-NI Term Expected term (in years) Equity securities FV-NI term. Cash and Cash Equivalents [Member] Cash and Cash Equivalents Long-term marketable securities Marketable Securities, Noncurrent Patent Costs Legal Costs, Policy [Policy Text Block] Intangible assets Deferred Tax Assets, Goodwill and Intangible Assets Temporary equity stock issued during period shares conversion of convertible securities. Temporary Equity Stock Issued During Period Shares Conversion Of Convertible Securities Entity Central Index Key Entity Central Index Key Deferred tax assets, increase in valuation allowance Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount Vesting of early exercised stock options Stock Issued During Period Value Vesting Of Early Exercised Stock Options Stock issued during period value, vesting of early exercised stock options. Accounting Policies [Abstract] Investments, Debt and Equity Securities [Abstract] Payment of development and regulatory milestone obligation Payment of Development and Regulatory Milestone Obligation Payment of Development and Regulatory Milestone Obligation Schedule Of Available For Sale Securities [Line Items] Debt Securities, Available-for-Sale [Line Items] Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment, Total Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment, Beginning Balance Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment, Ending Balance Less accumulated depreciation and amortization Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Schedule Of Property Plant And Equipment [Table] Property, Plant and Equipment [Table] Share-Based Compensation Arrangement by Share-Based Payment Award, Fair Value Assumptions, Expected Volatility Rate Expected volatility Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract] Measurement Frequency Measurement Frequency [Axis] Life Arc [Member] LifeArc. LifeArc License Agreement License Agreement [Member] License agreement. Stock-based Compensation Share-Based Payment Arrangement [Text Block] Subsequent Event [Table] General and Administrative Expense, Total General and administrative General and Administrative Expense Measurement Input Type Measurement Input Type [Domain] Organization, Consolidation and Presentation of Financial Statements [Abstract] Weighted-average exercise price, Outstanding at December 31, 2022 Weighted-average exercise price, Outstanding at December 31, 2021 Weighted-average exercise price, Outstanding at June 30, 2021 Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding, Weighted Average Exercise Price Research and Development Research and Development Expense [Member] Risk-free interest rate, minimum Share-Based Compensation Arrangement by Share-Based Payment Award, Fair Value Assumptions, Risk Free Interest Rate, Minimum Prepaid Expenses and Other Current Assets Forecast Forecast [Member] Total lease cost Total lease cost Total lease cost Options Early Exercised Subject to Future Vesting Options Early Exercised Subject To Future Vesting [Member] Options early exercised subject to future vesting. Operating lease assets obtained in exchange for lease obligation Right-of-Use Asset Obtained in Exchange for Operating Lease Liability 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] Accumulated Deficit Retained Earnings [Member] Security Deposit Security deposit paid Tax Credit Carryforward, Name [Domain] Shares issued Business Acquisition, Equity Interest Issued or Issuable, Number of Shares Money Market Funds Money Market Funds [Member] Measurement Input Type Measurement Input Type [Axis] Effective income tax rate Effective Income Tax Rate Reconciliation, Percent Property and equipment Property, Plant and Equipment, Gross Property, Plant and Equipment, Gross, Total Property, Plant and Equipment, Gross, Beginning Balance Property, Plant and Equipment, Gross, Ending Balance Noncash preferred stock purchase right liability. Noncash Preferred Stock Purchase Right Liability Preferred stock purchase right liability Number of litigations filed Loss Contingency, Number of Plaintiffs Stock vesting percentage Share-Based Compensation Arrangement by Share-Based Payment Award, Award Vesting Rights, Percentage Entity Interactive Data Current Entity Interactive Data Current Tax credit carryforwards Tax Credit Carryforward, Amount Entity Public Float Related Party Transactions Related Party Transactions Disclosure [Text Block] Supplemental disclosure of noncash investing and financing activity: Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract] Related Party Transactions [Abstract] 2023 Lessee, Operating Lease, Liability, to be Paid, Year One Concentration of Credit Risk and Off-Balance Sheet Risk Off-Balance-Sheet Credit Exposure, Policy [Policy Text Block] Leasehold Improvements Leasehold Improvements [Member] Discounts and offering costs Adjustments to Additional Paid in Capital, Stock Issued, Issuance Costs Preferred shares outstanding Temporary equity, shares outstanding Convertible preferred stock, beginning balance, shares Convertible preferred stock, ending balance, shares Temporary Equity, Shares Outstanding Unrealized losses 12 months or greater, Fair value Available of sale securities, unrealized loss position, greater than 12 months Debt Securities, Available-for-Sale, Continuous Unrealized Loss Position, 12 Months or Longer Proceeds from the issuance of common stock in initial public offering, net of discounts and offering costs Net proceeds received from initial public offering (IPO) Proceeds from Issuance Initial Public Offering Local Phone Number Local Phone Number Federal statutory income tax rate Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent Balance at the end of the year Balance at the beginning of the year Unrecognized Tax Benefits Novartis Pharma AG Novartis Pharma AG [Member] Novartis Pharma AG [Member] Summary of Financial Assets Measured at Fair Value on Recurring Basis Fair Value, Assets Measured on Recurring Basis [Table Text Block] Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Summary of Computation of Basic and Diluted Net Loss Per Share Stock vesting period Share-Based Compensation Arrangement by Share-Based Payment Award, Award Vesting Period Asana Merger Agreement Asana Merger Agreement [Member] Asana merger agreement. Contribution of common stock to Erasca Foundation Contribution Of Common Stock Contribution of common stock. Share Based Compensation Arrangement By Share Based Payment Award [Line Items] Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items] Lease Contractual Term [Axis] Shares Options exercisable at December 31, 2022 Shares Options exercisable at June 30, 2021 Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Exercisable, Number First Amendment to 2020 lease. First Amendment to Two Thousand and Twenty Lease [Member] First Amendment to 2020 Lease IPO IPO [Member] Proceeds from issuance of convertible preferred stock Proceeds from the issuance of convertible preferred stock, net of issuance costs Proceeds from Issuance of Convertible Preferred Stock Lessee, Operating Lease, Existence of Option to Extend [true false] Operating lease existence of option to extend [true false] Two thousand eighteen lease. Two Thousand Eighteen Lease [Member] 2018 Lease Share-based compensation, options granted that vest based on performance milestone Shares Granted Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Grants in Period, Gross ELS Purchase Agreement Emerge Life Sciences Purchase Agreement [Member] Emerge life sciences purchase agreement. COVID-19 Pandemic C O V I D19 Pandemic [Text Block] COVID-19 pandemic. Other liabilities Other Liabilities, Noncurrent Reverse stock split ratio Series B-1 convertible preferred shares converted into common stock Stockholders' Equity Note, Stock Split, Conversion Ratio Fair Value Measurement Inputs and Valuation Techniques [Abstract] Income Statement Location Income Statement Location [Domain] Risk-free Interest Rate Measurement Input, Risk Free Interest Rate [Member] Property, Plant and Equipment [Abstract] Number of restricted stock shares outstanding, Nonvested at December 31, 2022 Number of restricted stock shares outstanding, Nonvested at December 31, 2021 Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Nonvested, Number Tenant Improvement Allowance Included in Operating Lease Liabilities Tenant improvement allowance included in operating lease liabilities. Tenant improvement allowance included in operating lease liabilities Fair Value of Underlying Preferred Stock Measurement Input Fair Value Of Underlying Preferred Stock [Member] Measurement Input fair value of underlying preferred 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] Shares Outstanding at December 31, 2022 Shares Outstanding at December 31, 2021 Shares Outstanding at September 30, 2021 Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding, Number Share Price Share price per share Short-term marketable securities Marketable Securities, Current Document Fiscal Year Focus Document Fiscal Year Focus Adjustments to value of investment in equity securities Equity Securities Without Readily Determinable Fair Value, Impairment or Price Adjustment Amount Equity securities without readily determinable fair value, impairment or price adjustment amount. Share-based compensation, vesting rights description Share-Based Compensation Arrangement by Share-Based Payment Award, Award Vesting Rights 2024 Lessee, Operating Lease, Liability, to be Paid, Year Two Vesting Vesting [Domain] Cash payments in license agreement upon achievement of corporate milestone Cash payments in license agreement upon achievement of corporate milestone. Cash Payments in License Agreement Upon Achievement of Corporate Milestone Net loss per share, basic Earnings Per Share, Basic Earnings Per Share, Basic, Total Common stock, dividends declared Common Stock, Dividends, Per Share, Declared Assets Assets [Abstract] Net deferred tax assets Deferred Tax Assets, Net Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents [Abstract] Expected volatility, minimum Share-Based Compensation Arrangement by Share-Based Payment Award, Fair Value Assumptions, Expected Volatility Rate, Minimum Prepaid expenses and other current assets Prepaid Expense and Other Assets, Current Interest income Interest Income (Expense), Nonoperating, Net Financial Instrument [Axis] Long-Lived Tangible Asset Long-Lived Tangible Asset [Axis] Operating lease liabilities Deferred Tax Assets Operating Lease Liabilities Deferred tax assets, operating lease liabilities. Liabilities and Stockholders' Equity Liabilities and Equity [Abstract] Accrued Employee Benefits, Current Accrued compensation Cash paid for taxes Income Taxes Paid, Net Income Taxes Paid, Net, Total Property and Equipment, Net Property, Plant and Equipment, Policy [Policy Text Block] Antidilutive Securities, Name [Domain] Antidilutive Securities, Name Income Tax Authority [Axis] Valuation Approach and Technique [Axis] Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Net loss Net Income (Loss), Including Portion Attributable to Noncontrolling Interest, Total Share-based payment arrangement, withheld on behalf of employees for future purchase Share-based Payment Arrangement, Withheld on Behalf of Employees for Future Purchase Share-based payment arrangement, withheld on behalf of employees for future purchase. Current assets: Assets, Current [Abstract] MASSACHUSETTS MASSACHUSETTS Schedule of Significant Portions of Deferred Tax Assets and Deferred Tax Liabilities Schedule of Deferred Tax Assets and Liabilities [Table Text Block] Unrealized losses less than 12 months, Unrealized losses Unrealized Losses Less Than 12 months, Unrealized Losses Debt Securities, Available-for-Sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss Fair Value Hierarchy and NAV Fair Value Hierarchy and NAV [Domain] Safe harbor contribution expense Defined Contribution Plan, Employer Discretionary Contribution Amount Payables and Accruals [Abstract] Measurement Frequency Measurement Frequency [Domain] Katmai Pharmaceuticals, Inc. Katmai Pharmaceuticals Incorporation [Member] Katmai Pharmaceuticals, Inc. Changes in operating assets and liabilities: Increase (Decrease) in Operating Capital [Abstract] Provision for federal income taxes Federal Income Tax Expense (Benefit), Continuing Operations Federal Income Tax Expense (Benefit), Continuing Operations, Total Less: Tenant improvement allowance receivable Lessee Operating Lease Liability Tenant Improvement Allowance Receivable Lessee operating lease liability tenant improvement allowance receivable Related Party Transaction [Line Items] Entity Entity [Domain] Cover [Abstract] Product and Service [Domain] Product and Service Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward] 2027 Lessee, Operating Lease, Liability, to be Paid, Year Five Organization And Basis Of Presentation [Table] Organization And Basis Of Presentation [Table] Organization and basis of presentation. Number of restricted stock shares outstanding, Vested Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Vested in Period Stock issued during period in connection with licensing agreement value. Stock Issued During Period in Connection with Licensing Agreement Value Issuance of common stock in connection with license agreement Operating lease cancellation payment Operating Lease Cancellation Payment Operating lease cancellation payment. Current liabilities: Liabilities, Current [Abstract] Maximum Maximum [Member] Unrealized loss on marketable securities, net OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment, after Tax Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Table Text Block] Schedule of Stock-based Compensation Expense Issuance of common stock in connection with asset acquisition Issuance Of Common Stock In Connection With Asset Acquisition Issuance of common stock in connection with asset acquisition. Net cash used in investing activities Net Cash Provided by (Used in) Investing Activities Furniture and Fixtures Furniture and Fixtures [Member] Schedule Of Antidilutive Securities Excluded From Computation Of Earnings Per Share [Table] Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table] Shares Exercised Exercise of stock options, shares Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Exercises in Period Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers, Net Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers, Net, Total Measurement at fair value, transfers among Level 1, Level 2 or Level 3 Significant Unobservable Inputs (Level 3) Fair Value, Inputs, Level 3 [Member] Use of Estimates Use of Estimates, Policy [Policy Text Block] Total deferred tax liabilities Total deferred tax liabilities Deferred Tax Liabilities, Gross Exercise of stock options Stock Issued During Period, Value, Stock Options Exercised Segments Segment Reporting, Policy [Policy Text Block] Accrued expenses and other current and long-term liabilities Increase Decrease In Accrued Expenses And Other Current And Long-term Liabilities Increase decrease in accrued expenses and other current and long-term liabilities. Estimated useful lives of assets Property, Plant and Equipment, Useful Life Common stock, shares authorized Common Stock, Shares Authorized Trading Symbol Trading Symbol Temporary Equity Stock Issued During Period Value Conversion Of Convertible Securities Temporary equity stock issued during period value conversion of convertible securities Amounts accrued for in-process research and development expenses Amounts accrued for in-process research and development expenses Subsequent Event Type Subsequent Event Type [Axis] Other, net Deferred Tax Assets, Other Deferred tax assets contribution of common stocks. Deferred Tax Assets Contribution Of Common Stocks Contribution of common stock Repurchases of early exercised stock options and restricted stock. Repurchases of Early Exercised Stock Options and Restricted Stock Repurchases of early exercised stock options and restricted stock, Shares Balance Sheet Location Balance Sheet Location [Axis] Comprehensive loss Comprehensive Income (Loss), Net of Tax, Attributable to Parent Risk-free interest rate Share-Based Compensation Arrangement by Share-Based Payment Award, Fair Value Assumptions, Risk Free Interest Rate Accounts Payable, Current, Total Accounts payable Accounts Payable, Current Available for sale securities, Unrealized losses Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax Two thousand twenty one lease. Two Thousand Twenty One Lease [Member] 2021 Lease Plan Name Plan Name [Axis] Schedule of Related Party Transactions, by Related Party [Table] Long-Lived Tangible Asset Long-Lived Tangible Asset [Domain] Common stock, par value Common Stock, Par or Stated Value Per Share Entity Well-known Seasoned Issuer Issuance of common stock in connection with asset acquisition, shares Stock Issued During Period, Shares, Acquisitions 2020 Lease Two Thousand Twenty Lease [Member] Two thousand twenty lease. Variable lease costs Variable Lease, Cost Prepaid rent Prepaid Rent Conversion of convertible preferred stock into common stock upon initial public offering Stock Issued During Period, Value, Conversion of Convertible Securities Share-based compensation, liabilities associated with shares issued with repurchase rights Deferred Compensation Share-Based Arrangements, Liability, Current Comprehensive Income (Loss) Comprehensive Income, Policy [Policy Text Block] Sales milestone payments obligation Sales Milestone Payments Obligation Sales milestone payments obligation. Restricted stock granted Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period Issuance of common stock in connection with asset acquisition Stock Issued During Period, Value, Acquisitions Property and Equipment, Net Property, Plant and Equipment Disclosure [Text Block] Research and development Research and Development Expense (Excluding Acquired in Process Cost) Weighted-average exercise price, Granted Share-Based Compensation Arrangements by Share-Based Payment Award, Options, Grants in Period, Weighted Average Exercise Price Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Anti-dilutive securities excluded from calculation of diluted net loss per share Repurchases of restricted stock Repurchases of restricted stock Repurchases of Restricted Stock Repurchases of restricted stock.