Summary of Significant Accounting Policies Significant Accounting Policies [Text Block] Statistical Measurement [Domain] Statistical Measurement [Domain] Investments in Marketable Securities Investment, Policy [Policy Text Block] Thereafter Lessee, Operating Lease, Liability, to be Paid, after Year Five Schedule of Debt Securities, Fair Value of U.S. Treasury Securities and Money Market Fund Debt Securities, Available-for-Sale [Table Text Block] Operating Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration] Operating Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration] Award Timing Predetermined Award Timing Predetermined [Flag] Unrealized gain on available for sale securities, net of tax OCI, Debt Securities, Available-for-Sale, Gain (Loss), after Adjustment, Tax Entity File Number Entity File Number Additional paid-in capital Additional Paid-in Capital [Member] Debt Issuance Costs Debt, Policy [Policy Text Block] 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Arrangement, Expense Schedule of Property and Equipment, Net Property, Plant and Equipment [Table Text Block] Ordinary shares, shares authorized (in shares) Common Stock, Shares Authorized Segment Reporting, Asset Reconciling Item [Line Items] Segment Reporting, Asset Reconciling Item [Line Items] Maximum number of undisclosed targets to research products Contract With Customer, Maximum Number Of Undisclosed Targets To Research Products Contract With Customer, Maximum Number Of Undisclosed Targets To Research Products Issuance of ordinary shares, net of issuance costs (in shares) Stock Issued During Period, Shares, New Issues Current assets: Assets, Current [Abstract] Forfeited (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Forfeitures in Period Defined contribution plan, minimum employee contribution, (as a percent) Defined Contribution Plan, Minimum Employee Contribution, Percent Defined Contribution Plan, Minimum Employee Contribution, 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adjustment for realized net gain on available for sale marketable securities included in net loss, net of tax of $0.8 million in 2025 and $0.4 million in 2024 Reclassification adjustment for realized net gain on available for sale marketable securities included in net loss, net of tax Reclassification from AOCI, Current Period, Net of Tax, Attributable to Parent Other Deferred Tax Assets, Other Maximum Maximum [Member] Exercisable at end of period (in dollars per share) Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Exercisable, Weighted Average Exercise Price General and administrative General and Administrative Expense [Member] Accounting Policies [Abstract] Remaining shares reserved for issuance (in shares) Share Repurchase Program, Remaining Authorized, Number of Shares Defined contribution plan, minimum employer contribution, (as a percent) Defined Contribution Plan, Minimum Employer Contribution, Percent Defined Contribution Plan, Minimum Employer Contribution, Percent Schedule of Lessee, Operating Lease, Liability, Maturity Lessee, Operating Lease, Liability, to be Paid, Maturity [Table Text Block] Restricted Stock Awards Restricted Stock [Member] Non-PEO NEO Average Total Compensation Amount Non-PEO NEO Average Total Compensation Amount Debt Instrument [Line Items] Debt Instrument [Line Items] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of Share-Based Compensation Arrangements by Share-Based Payment Award [Table] Adjustment to Non-PEO NEO Compensation Footnote Adjustment to Non-PEO NEO Compensation Footnote [Text Block] Pay vs Performance Disclosure [Line Items] Total operating lease liabilities Total operating lease liabilities Operating Lease, Liability Foreign currency translation adjustments Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax, Portion Attributable to Parent Forgone Recovery due to Disqualification of Tax Benefits, Amount Forgone Recovery due to Disqualification of Tax Benefits, Amount Total undiscounted amounts Lessor, Operating Lease, Payment to be Received Maximum cash covenant of outstanding principal balance of the term loan (as a percent) Debt Instrument, Covenant, Maximum Cash Threshold Debt Instrument, Covenant, Maximum Cash Threshold Liabilities: Liabilities [Abstract] Non-Rule 10b5-1 Arrangement Terminated Non-Rule 10b5-1 Arrangement Terminated [Flag] Loss before income taxes Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest Entity Shell Company Entity Shell Company Total principal payments, including End of Term Charge Long-Term Debt, Gross And End Of Term Charge Long-Term Debt, Gross And End Of Term Charge Other noncurrent liabilities Other Liabilities, Noncurrent Schedule of Long-term Debt Instruments [Table] Schedule of Long-Term Debt Instruments [Table] Proceeds from issuance of debt Proceeds from Issuance of Debt Shareholders’ equity Statement of Stockholders' Equity [Abstract] Statement of Cash Flows [Abstract] Company Selected Measure Amount Company Selected Measure Amount 2028 Lessee, Operating Lease, Liability, to be Paid, Year Three Award Timing MNPI Considered Award Timing MNPI Considered [Flag] Debt issuance costs Debt Issuance Costs, Gross Total comprehensive (loss) income Comprehensive Income (Loss), Net of Tax, Attributable to Parent Long-term investments Debt Securities, Available-for-Sale, Excluding Accrued Interest, Noncurrent Losses surrendered for UK research tax incentive Effective Income Tax Rate Reconciliation, Losses Surrendered for Tax Incentive, Percent Effective Income Tax Rate Reconciliation, Losses Surrendered for Tax Incentive, Percent Name Measure Name Balance as of January 1, 2025 Balance as of December 31, 2025 Restructuring Reserve Schedule of Income before Income Tax, Domestic and Foreign Schedule of Income before Income Tax, Domestic and Foreign [Table Text Block] UK Income (Loss) from Continuing Operations before Income Taxes, Domestic Schedule of Share-based Compensation Expense Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Table Text Block] Amortization of discount of marketable securities Investment Income, Net, Amortization of Discount and Premium Operating lease Less: current portion Operating Lease, Liability, Current Secured Debt Secured Debt [Member] Additional cash payment (in USD per share) Common Stock, Additional Cash Payment Common Stock, Additional Cash Payment Document Fiscal Period Focus Document Fiscal Period Focus Collaborative Arrangements Collaborative Arrangement, Accounting Policy [Policy Text Block] Award Timing Method Award Timing Method [Text Block] Office furniture Furniture and Fixtures [Member] U.S. Treasury securities, amortized cost Debt Securities, Available-for-Sale, Amortized Cost, Excluding Accrued Interest, after Allowance for Credit Loss Award Type [Axis] Award Type [Axis] Loan and Security Agreement (carried at amortized cost) Long-Term Debt Total assets Assets Collaborative Arrangement and Arrangement Other than Collaborative [Line Items] Collaborative Arrangement and Arrangement Other than Collaborative [Line Items] Share-Based Compensation Share-Based Payment Arrangement [Policy Text Block] Trading Symbol Trading Symbol 2029 Lessee, Operating Lease, Liability, to be Paid, Year Four Vested (in dollars per share) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value Cash, Cash Equivalents, and Restricted Cash Cash and Cash Equivalents, Restricted Cash and Cash Equivalents, Policy [Policy Text Block] Increase in valuation allowance Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Percent Operating Loss Carryforwards [Table] Operating Loss Carryforwards [Table] Income Taxes Income Tax, Policy [Policy Text Block] Return to provision adjustments Effective Income Tax Rate Reconciliation, Return To Provision Adjustments, Percent Effective Income Tax Rate Reconciliation, Return To Provision Adjustments, Percent Entity Address, City or Town Entity Address, City or Town Cash flows from operating activities: Cash Provided by (Used in) Operating Activity, Including Discontinued Operation [Abstract] U.S. research & development tax credits Effective Income Tax Rate Reconciliation, Tax Credit, Research, Percent Other segment items Segment Reporting, Other Segment Item, Amount Effect of exchange rate on cash, cash equivalents, and restricted cash Effect of Exchange Rate on Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Continuing Operation Deferred tax assets, net of allowance Deferred Tax Assets, Net of Valuation Allowance Non-PEO NEO Average Compensation Actually Paid Amount Non-PEO NEO Average Compensation Actually Paid Amount Statement of Income Location, Balance [Domain] Statement of Income Location, Balance [Domain] Restricted stock units Restricted Stock Units Restricted Stock Units (RSUs) [Member] Compensation Actually Paid vs. Other Measure Compensation Actually Paid vs. Other Measure [Text Block] Assets Assets, Fair Value Disclosure [Abstract] Gregory Weinhoff [Member] Gregory Weinhoff Accrued contract termination costs Restructuring Costs Entity Emerging Growth Company Entity Emerging Growth Company 2028 Long-Term Debt, Maturity, Year Three Prepayment fee, period two Debt Instrument, Prepayment Fee, Period Two Debt Instrument, Prepayment Fee, Period Two Research and development Research and Development Expense (Excluding Acquired in Process Cost) Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Debt Securities, Available-for-Sale [Line Items] Debt Securities, Available-for-Sale [Line Items] Beginning balance (in shares) Ending balance (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding, Number Change in Fair Value as of Vesting Date of Prior Year Equity Awards Vested in Covered Year Change in Fair Value as of Vesting Date of Prior Year Equity Awards Vested in Covered Year [Member] Significant other observable inputs (Level 2) Fair Value, Inputs, Level 2 [Member] Document Financial Statement Error Correction [Flag] Document Financial Statement Error Correction [Flag] Restructuring Reserve [Roll Forward] Restructuring Reserve [Roll Forward] Insider Trading Policies and Procedures Not Adopted Insider Trading Policies and Procedures Not Adopted [Text Block] Operating Leases Lessee, Operating Lease, Liability, to be Paid, Fiscal Year Maturity [Abstract] Ordinary shares, shares outstanding (in shares) Beginning balance (in shares) Ending balance (in shares) Common Stock, Shares, Outstanding Schedule of Components of Income Tax Provision Schedule of Components of Income Tax Expense (Benefit) [Table Text Block] Plan Name [Axis] Plan Name [Axis] Property and Equipment, net Property, Plant and Equipment, Policy [Policy Text Block] Document Information [Table] Document Information [Table] PEO PEO [Member] Severance-Related Employee Severance [Member] U.S. Internal Revenue Service (IRS) [Member] UK His Majesty's Revenue and Customs (HMRC) [Member] Interest income Interest income Investment Income, Interest American Depositary Shares American Depositary Shares [Member] American Depositary Shares Non-program specific expenses: Other R&D Expenses [Abstract] Other R&D Expenses Valuation allowance (decrease) increase Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount Share-based payment awards issued in period (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Shares Issued in Period Income tax liability Accrued Income Taxes, Current Changes in operating assets and liabilities: Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity, Increase (Decrease) in Operating Capital [Abstract] Stock option exercises Stock Issued During Period, Value, Stock Options Exercised Dividends or Other Earnings Paid on Equity Awards not Otherwise Reflected in Total Compensation for Covered Year Dividends or Other Earnings Paid on Equity Awards not Otherwise Reflected in Total Compensation for Covered Year [Member] Expected stock price volatility Share-Based Compensation Arrangement by Share-Based Payment Award, Fair Value Assumptions, Expected Volatility Rate Number of shares issued per ordinary share (in shares) Sale Of Stock, Number Of Shares Issued Per Ordinary Share Sale Of Stock, Number Of Shares Issued Per Ordinary Share Accumulated deficit Retained Earnings [Member] Prepaid expenses and other current assets Prepaid expenses and other current assets Prepaid Expense and Other Assets, Current Income Tax Jurisdiction [Axis] Income Tax Jurisdiction [Axis] Number of Shares Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] Schedule of Accrued Expenses and Other Current Liabilities Schedule of Accrued Liabilities [Table Text Block] Entity Address, Postal Zip Code Entity Address, Postal Zip Code Restatement Determination Date Restatement Determination Date Share-Based Payment Arrangement [Abstract] Cash, cash equivalents, and restricted cash at beginning of period Cash, cash equivalents, and restricted cash at end of period Total Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Continuing Operation Income Statement [Abstract] Income tax expense Income tax expense (benefit) Income tax (expense) benefit Income Tax Expense (Benefit) Debt instrument, basis spread on variable rate Debt Instrument, Basis Spread on Variable Rate Research and development costs Prepaid Research and Development Costs Prepaid Research and Development Costs Purchases of investments in marketable securities Payments to Acquire Marketable Securities Research and development tax incentive Income Tax, Research And Development Tax Incentives Income Tax, Research And Development Tax Incentives Sale of Stock [Domain] Sale of Stock [Domain] Document Information [Line Items] Document Information [Line Items] Pension Adjustments Service Cost Pension Adjustments Service Cost [Member] Product and Service [Domain] Product and Service [Domain] Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Property and equipment, at cost Property, Plant and Equipment, Gross 2028 Lessor, Operating Lease, Payment to be Received, Year Three Restatement does not require Recovery Restatement Does Not Require Recovery [Text Block] Organization, Consolidation and Presentation of Financial Statements [Abstract] Program Termination Costs Restructuring and Related Activities Disclosure [Text Block] Defined contribution plan, minimum contribution, (as a percent) Defined Contribution Plan, Minimum Contribution, Percent Defined Contribution Plan, Minimum Contribution, Percent Compensation Actually Paid vs. Company Selected Measure Compensation Actually Paid vs. Company Selected Measure [Text Block] Proceeds from option exercises Proceeds from Stock Options Exercised City Area Code City Area Code Award Timing, How MNPI Considered Award Timing, How MNPI Considered [Text Block] All Trading Arrangements All Trading Arrangements [Member] Equity Awards Adjustments, Footnote Equity Awards Adjustments, Footnote [Text Block] Total Shareholder Return Vs Peer Group Total Shareholder Return Vs Peer Group [Text Block] Options vested and expected to vest, weighted-average remaining contractual term (in years) Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Vested and Expected to Vest, Outstanding, Weighted Average Remaining Contractual Term Accrued expenses and other current liabilities Accrued expenses and other current liabilities Accrued Liabilities, Current Research and development costs Accrued Research And Development Expense, Current Accrued Research And Development Expense, Current Unvested beginning balance (in shares) Unvested ending balance (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Nonvested, Number Commitments and Contingencies Disclosure [Abstract] Maximum additional potential option exercise fee Revenue, Remaining Performance Obligation, Variable Consideration Amount Revenue, Remaining Performance Obligation, Variable Consideration Amount Cash flows from investing activities: Cash Provided by (Used in) Investing Activity, Including Discontinued Operation [Abstract] General and administrative General and administrative expenses General and Administrative Expense Unrecognized compensation expense related to unvested stock option awards Share-Based Payment Arrangement, Nonvested Award, Option, Cost Not yet Recognized, Amount Pay vs Performance Disclosure Pay vs Performance Disclosure [Table] Net cash used in operating activities Cash Provided by (Used in) Operating Activity, Including Discontinued Operation Defined contribution plan, employer matching contribution, (as a percent) Defined Contribution Plan, Employer Matching Contribution, Percent of Match Additional shares authorized each year (as a percent) Share-based Compensation Arrangement by Share-based Payment Award, Percent of Additional Shares Authorized Each Year Share-based Compensation Arrangement by Share-based Payment Award, Percent of Additional Shares Authorized Each Year Prepayment fee, period one Debt Instrument, Prepayment Fee, Period One Debt Instrument, Prepayment Fee, Period One Debt securities, available-for-sale, fair value Debt Securities, Available-for-Sale, Excluding Accrued Interest Potential additional development and sales milestone Revenue From Contract With Customer, Potential Additional Development, Regulatory And Sales Milestone Payments Revenue From Contract With Customer, Potential Additional Development, Regulatory And Sales Milestone Payments Property and equipment useful life (in years) Property, Plant and Equipment, Useful Life Subsequent Event Subsequent Event [Member] Schedule of Assumptions Used to Estimate Fair Value of Stock Option Awards Schedule of Share-Based Payment Award, Stock Options, Valuation Assumptions [Table Text Block] Total operating lease cost Lease, Cost Equity Valuation Assumption Difference, Footnote Equity Valuation Assumption Difference, Footnote [Text Block] Schedule of Lease, Cost Lease, Cost [Table Text Block] PEO Total Compensation Amount PEO Total Compensation Amount Depreciation expense Depreciation Long-term Debt, Type [Axis] Long-Term Debt, Type [Axis] Operating loss carryforwards, subject to expiration Operating Loss Carryforwards, Subject To Expiration Operating Loss Carryforwards, Subject To Expiration Vested and expected to vest as end of period (in dollars per share) Share-Based Compensation Arrangement by Share-Based Payment Award, Options, 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Adopted [Flag] Number of reportable segments Number of Reportable Segments Supplemental disclosure: Supplemental Cash Flow Information [Abstract] Restructuring Cost and Reserve [Line Items] Restructuring Cost and Reserve [Line Items] Entity Address, Country Entity Address, Country Other Performance Measure, Amount Other Performance Measure, Amount Weighted-Average Exercise Price Per Share Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract] Antidilutive Security, Excluded EPS Calculation [Table] Antidilutive Security, Excluded EPS Calculation [Table] Fair Value Measurement Fair Value Measurement, Policy [Policy Text Block] 2026 Lessor, Operating Lease, Payment to be Received, Year One Retirement Plans Pension and Other Postretirement Plans, Policy [Policy Text Block] Total current liabilities Liabilities, Current Receivable per company share (in USD per share) Common Stock, Receivable Per Company Share Common Stock, Receivable Per Company Share Individual: Individual [Axis] Defined contribution plan, charges Defined Contribution Plan, Cost Restricted cash Restricted Cash Sublease Income Lessor, Operating Lease, Payment to be Received, Fiscal Year Maturity [Abstract] Income Tax Jurisdiction [Domain] Income Tax Jurisdiction [Domain] Other Other Assets, Current Document Annual Report Document Annual Report Research and development Research and Development Expense [Member] Net cash provided by (used in) investing activities Cash Provided by (Used in) Investing Activity, Including Discontinued Operation Aggregate Change in Present Value of Accumulated Benefit for All Pension Plans Reported in Summary Compensation Table Aggregate Change in Present Value of Accumulated Benefit for All Pension Plans Reported in Summary Compensation Table [Member] Purchase obligation, to be paid within one year Purchase Obligation, to be Paid, Year One Floor rate Debt Instrument, Floor Rate Debt Instrument, Floor Rate Genmab A/S Genmab A/S [Member] Genmab A/S Interest paid Interest Paid, Excluding Capitalized Interest, Operating Activity Document Fiscal Year Focus Document Fiscal Year Focus Basis of Presentation and Consolidation Basis of Accounting, Policy [Policy Text Block] Investments above with unrealized loss, gross unrealized losses Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, Before Tax, Without Accumulated Unrealized Loss Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, Before Tax, Without Accumulated Unrealized Loss Operating lease right-of-use assets Operating lease, right-of-use asset Operating Lease, Right-of-Use Asset Forgone Recovery, Explanation of Impracticability Forgone Recovery, Explanation of Impracticability [Text Block] Effective income tax rate Effective Income Tax Rate Reconciliation, Percent Entity Interactive Data Current Entity Interactive Data Current Operating lease cost Operating Lease, Cost Plan Name [Domain] Plan Name [Domain] Unrecognized compensation expense recognition period (in years) Expected weighted average recognition period Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition Stock option exercises (in shares) Exercised (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Exercises in Period Valuation allowance Deferred Tax Assets, Valuation Allowance License and other revenue Revenue from Contract with Customer [Policy Text Block] Aggregate intrinsic value of exercisable Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Exercisable, Intrinsic Value Less: Segment Reconciliation [Abstract] Purchase obligation Purchase Obligation Segment Information Segment Reporting Disclosure [Text Block] Aggregate Intrinsic Value (in millions) Share-Based Compensation Arrangement By Share-Based Payment Award, Aggregate Intrinsic Value [Abstract] Share-Based Compensation Arrangement By Share-Based Payment Award, Aggregate Intrinsic Value 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] U.S. Treasury securities US Treasury Securities [Member] Tax loss carryforwards Deferred Tax Assets, Operating Loss Carryforwards Current Current Federal Tax Expense (Benefit) Long-Lived Tangible Asset [Axis] Long-Lived Tangible Asset [Axis] Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Compensation Actually Paid vs. Total Shareholder Return Compensation Actually Paid vs. Total Shareholder Return [Text Block] Shares reserved for issuance (in shares) Share Repurchase Program, Authorized, Number of Shares Fair Value, Recurring and Nonrecurring [Table] Fair Value, Recurring and Nonrecurring [Table] Schedule of Lessor, Operating Lease, Liability, Maturity Lessor, Operating Lease, Payment to be Received, Maturity [Table Text Block] Leases Lessee, Leases [Policy Text Block] Deferred tax asset Deferred Income Tax Assets, Net Depreciation and amortization Depreciation, Depletion and Amortization Other non-current assets Other Assets, Noncurrent Interest payable Interest Payable, Current Entity Central Index Key Entity Central Index Key PEO Name PEO Name Schedule of Maturities of Long-Term Debt Schedule of Maturities of Long-Term Debt [Table Text Block] License and other revenue Revenue Revenues Aggregate net proceeds from shares sold Sale of Stock, Consideration Received on Transaction Prior Year End Fair Value of Equity Awards Granted in Any Prior Year that Fail to Meet Applicable Vesting Conditions During Covered Year Prior Year End Fair Value of Equity Awards Granted in Any Prior Year that Fail to Meet Applicable Vesting Conditions During Covered Year [Member] Outstanding Aggregate Erroneous Compensation Amount Outstanding Aggregate Erroneous Compensation Amount Arrangement Duration Trading Arrangement Duration Computer equipment Computer Equipment [Member] Segments [Axis] Segments [Axis] Investments above with unrealized loss, amortized cost Debt Securities, Available-for-Sale, Amortized Cost, Excluding Accrued Interest, After Allowance For Credit Loss, With Accumulated Unrealized Loss Debt Securities, Available-for-Sale, Amortized Cost, Excluding Accrued Interest, After Allowance For Credit Loss, With Accumulated Unrealized Loss Prepaid expenses and other assets Increase (Decrease) in Prepaid Expense and Other Assets Number of debt securities Number Of Debt Securities Number Of Debt Securities Exercise Price Award Exercise Price Entity Filer Category Entity Filer Category Local Phone Number Local Phone Number Class of Stock [Domain] Class of Stock [Domain] Maximum aggregate development and regulatory milestone payments Collaborative Arrangement, Rights and Obligations, Maximum Aggregate Development and Regulatory Milestone Payments Collaborative Arrangement, Rights and Obligations, Maximum Aggregate Development and Regulatory Milestone Payments Additional 402(v) Disclosure Additional 402(v) Disclosure [Text Block] Unrecognized compensation expense excluding options Share-Based Payment Arrangement, Nonvested Award, Excluding Option, Cost Not yet Recognized, Amount Collaborative Arrangement and Arrangement Other than Collaborative [Domain] Collaborative Arrangement and Arrangement Other than Collaborative [Domain] Statutory tax rate benefit Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent Share price (in dollars per share) Share Price Other, net Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity, Other Item Subsequent Event Type [Axis] Subsequent Event Type [Axis] Share-based Compensation Share-Based Payment Arrangement [Text Block] Rent expense, year 10 Operating Lease, Expense, Year 10 Operating Lease, Expense, Year 10 Minimum cash covenant of outstanding principal balance of the term loan (as a percent) Debt Instrument, Covenant Minimum Cash Threshold Debt Instrument, Covenant Minimum Cash Threshold Cash and cash equivalents and short-term investments Cash and Cash Equivalents and Short Term Investments Cash and Cash Equivalents and Short Term Investments Assets Assets: Assets [Abstract] Long term debt (Note 6) Long-Term Debt, Excluding Current Maturities Credit Facility [Axis] Credit Facility [Axis] Underlying Security Market Price Change Underlying Security Market Price Change, Percent Statement of Financial Position Location, Balance [Axis] Statement of Financial Position Location, Balance [Axis] Entity Address, Address Line Three Entity Address, Address Line Three Debt Instrument [Axis] Debt Instrument [Axis] Forfeited (in dollars per share) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value Fair Value of Financial Instruments Fair Value Disclosures [Text Block] Loss on extinguishment of debt Loss on extinguishment of debt Loss on extinguishment of debt Loss on extinguishment of debt Gain (Loss) on Extinguishment of Debt Deferred tax assets: Deferred Tax Assets, Net [Abstract] Credit Facility [Domain] Credit Facility [Domain] Vesting Date Fair Value of Equity Awards Granted and Vested in Covered Year Vesting Date Fair Value of Equity Awards Granted and Vested in Covered Year [Member] Entity Address, Address Line One Entity Address, Address Line One 2021 Plan 2021 Plan [Member] 2021 Plan Entity Address, Address Line Two Entity Address, Address Line Two Accumulated other comprehensive income AOCI Attributable to Parent [Member] Stated interest rate Debt Instrument, Interest Rate, Stated Percentage Foreign Foreign Income Tax Expense (Benefit) [Abstract] Foreign Income Tax Expense (Benefit) Shares withheld to pay employee withholding tax on equity awards (in shares) Share-Based Payment Arrangement, Shares Withheld for Tax Withholding Obligation Operating lease liabilities Operating lease liabilities, net of current portion Lease liabilities, net of current portion Operating Lease, Liability, Noncurrent Entity Voluntary Filers Entity Voluntary Filers Fair Value as of Grant Date Award Grant Date Fair Value Entity Registrant Name Entity Registrant Name Purchase obligation, to be paid, over one to three years Purchase Obligation, to be Paid, Year One through Three Purchase Obligation, to be Paid, Year One through Three Stock Price or TSR Estimation Method Stock Price or TSR Estimation Method [Text Block] Investments above with unrealized loss, amortized cost Debt Securities, Available-for-Sale, Amortized Cost, Excluding Accrued Interest, After Allowance For Credit Loss, Without Accumulated Unrealized Loss Debt Securities, Available-for-Sale, Amortized Cost, Excluding Accrued Interest, After Allowance For Credit Loss, Without Accumulated Unrealized Loss Personnel expenses Labor and Related Expense Amortization expense Capitalized Computer Software, Amortization Granted (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period Forfeited (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Forfeited in Period Total Assets, Fair Value Disclosure The fair value of LSA, classified as Level 2 under ASC Topic 820 Long-Term Debt, Fair Value Number of debt securities, loss position Debt Securities, Available-for-Sale, Unrealized Loss Position, Number of Positions Changed Peer Group, Footnote Changed Peer Group, Footnote [Text Block] Interest receivable Interest Receivable, Current Counterparty Name [Domain] Counterparty Name [Domain] Change in fair value of financial instruments Financial Instruments Gain (Loss) From Change In Fair Value Financial Instruments Gain (Loss) From Change In Fair Value 2027 Lessee, Operating 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Cost Recognition Accumulated other comprehensive income Accumulated Other Comprehensive Income (Loss), Net of Tax Country Region Country Region 2026 Long-Term Debt, Maturity, Year One Aggregate intrinsic value of vested and expected to vest Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Vested and Expected to Vest, Outstanding, Aggregate Intrinsic Value Financial Instruments [Domain] Financial Instruments [Domain] Auditor Firm ID Auditor Firm ID Segments [Domain] Segments [Domain] Statement of Income Location, Balance [Axis] Statement of Income Location, Balance [Axis] Non-UK Income (Loss) from Continuing Operations before Income Taxes, Foreign Capitalized Software Capitalized Software [Member] Capitalized Software Cash and Cash Equivalent [Table] Cash and Cash Equivalent [Table] Aggregate Pension Adjustments Service Cost Aggregate Pension Adjustments Service Cost [Member] Fair Value Hierarchy and NAV [Domain] Fair Value Hierarchy and NAV [Domain] Statement of Financial Position Location, Balance [Domain] Statement of Financial Position Location, Balance [Domain] Amortization of debt issuance costs and exit fee of long-term debt Amortization of Debt Issuance Costs and Discounts Minimum Minimum [Member] Income Tax Authority, Name [Domain] Income Tax Authority, Name [Domain] Less: Accumulated depreciation Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Net Loss Per Ordinary Share Earnings Per Share, Policy [Policy Text Block] Company Selected Measure Name Company Selected Measure Name Debt Debt Disclosure [Text Block] Aggregate Available Trading Arrangement, Securities Aggregate Available Amount Accounts payable Accounts Payable, Current Deferred tax liabilities: Deferred Tax Liabilities, Net [Abstract] Operating lease payments reducing operating lease liabilities Operating Lease, Payments Stock Appreciation Rights (SARs) Stock Appreciation Rights (SARs) [Member] All Executive Categories All Executive Categories [Member] Schedule of Deferred Tax Assets and Liabilities Schedule of Deferred Tax Assets and Liabilities [Table Text Block] Ordinary shares: £0.002 nominal value: 184,469,623 shares authorized; 149,228,068 shares issued and outstanding at December 31, 2025 and 132,631,587shares issued and outstanding at December 31, 2024 Common Stock, Value, Issued Current Current Foreign Tax Expense (Benefit) Short-term investments Short-Term Investments Commitments and Contingencies Commitments and Contingencies Disclosure [Text Block] Tax incentive receivable Increase (Decrease) In Tax Incentive Receivables Increase (Decrease) In Tax Incentive Receivables Weighted average ordinary shares outstanding - diluted (in shares) Weighted Average Number of Shares Outstanding, Diluted Segments Segment Reporting, Policy [Policy Text Block] Commitments and contingencies (Note 7) Commitments and Contingencies Non-GAAP Measure Description Non-GAAP Measure Description [Text Block] Reconciliation of 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Loss Carryforwards and Research Tax Credits Summary of Operating Loss Carryforwards and Research Tax Credits [Table Text Block] Summary of Operating Loss Carryforwards and Research Tax Credits Income Taxes Income Tax Disclosure [Text Block] Balance Sheet Components Supplemental Balance Sheet Disclosures [Text Block] Awards Close in Time to MNPI Disclosures, Table Awards Close in Time to MNPI Disclosures [Table Text Block] Revenue from Contract with Customer [Abstract] Investments above with no unrealized loss, gross unrealized gains Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Gain, Before Tax, With Accumulated Unrealized Loss Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Gain, Before Tax, With Accumulated Unrealized Loss Short term lease cost Short-Term Lease, Cost Options exercisable, weighted-average remaining contractual term (in years) Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Exercisable, Weighted Average 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Receivable, Current Contract Termination Contract Termination [Member] Fair Value Disclosures [Abstract] Purchase of property and equipment Payments to Acquire Property, Plant, and Equipment Vested and expected to vest at end of period (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Vested and Expected to Vest, Outstanding, Number Name Forgone Recovery, Individual Name Reversal of charge Restructuring Reserve, Accrual Adjustment Contractual term (in years) Share-Based Compensation Arrangement by Share-Based Payment Award, Expiration Period Total current assets Assets, Current Statistical Measurement [Axis] Statistical Measurement [Axis] Year-over-Year Change in Fair Value of Equity Awards Granted in Prior Years That are Outstanding and Unvested Year-over-Year Change in Fair Value of Equity Awards Granted in Prior Years That are Outstanding and Unvested [Member] Underwriter Offering Underwriter Offering [Member] Underwriter Offering Debt average interest rate (as a percent) Debt, Weighted Average Interest Rate Operating loss carryforwards and research tax credits Operating Loss Carryforwards and Research Tax Credits Operating Loss Carryforwards and Research Tax Credits Percentage of shares issued and outstanding (as a percent) Share-Based Compensation Arrangement by Share-Based Payment Award, Percentage of Outstanding Stock Maximum Aggregate Erroneous Compensation Amount Aggregate Erroneous Compensation Amount Karen Anderson [Member] Karen Anderson Total intrinsic value of options exercised Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Exercises in Period, Intrinsic Value Payment of employee withholding taxes related to withheld shares for stock based compensation plans Payment, Tax Withholding, Share-Based Payment Arrangement Peer Group Issuers, Footnote Peer Group Issuers, Footnote [Text Block] Other comprehensive (loss) income: Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent, Alternative [Abstract] Erroneous Compensation Analysis Erroneous Compensation Analysis [Text Block] Other comprehensive (loss) income Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent Current liabilities: Liabilities, Current [Abstract] Research and development credits Deferred Tax Assets, Tax Credit Carryforwards, Research 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] Lessee, Lease, Description [Line Items] Lessee, Lease, Description [Line Items] Vesting of ordinary shares (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options and Restricted Stock Units, Vested in Period Share-based Compensation Arrangement by Share-based Payment Award, Options and Restricted Stock Units, Vested in Period Unrealized gain on available for sale securities, net of tax of $0.1 million in 2025 and $0.8 million in 2024 Unrealized gain on available for sale securities, net of tax OCI, Debt Securities, Available-for-Sale, Gain (Loss), before Adjustment, after Tax Rule 10b5-1 Arrangement Terminated Rule 10b5-1 Arrangement Terminated [Flag] Quoted prices in active markets for identical assets (Level 1) Fair Value, Inputs, Level 1 [Member] Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items] Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Line Items] Foreign currency transaction gain (loss) Gain (Loss), Foreign Currency Transaction, before Tax Accrued expenses and other liabilities Increase (Decrease) in Accrued Liabilities Net loss per ordinary share - diluted (in dollars per share) Earnings Per Share, Diluted Erroneously Awarded Compensation Recovery Erroneously Awarded Compensation Recovery [Table] 2030 Lessor, Operating Lease, Payment to be Received, Year Five Title of 12(b) Security Title of 12(b) Security Lessee, Lease, Description [Table] Lessee, Lease, Description [Table] Insurance related expenses Prepaid Insurance Shares sold in offering (in shares) Sale of Stock, Number of Shares Issued in Transaction Long-Term Debt, Fiscal Year Maturity [Abstract] Long-Term Debt, Fiscal Year Maturity [Abstract] 2030 Lessee, Operating Lease, Liability, to be Paid, Year Five Investments above with no unrealized loss, fair value Debt Securities, Available-for-Sale, Excluding Accrued Interest, With Accumulated Unrealized Loss Debt Securities, Available-for-Sale, Excluding Accrued Interest, With Accumulated Unrealized Loss Auditor Location Auditor Location Schedule of Antidilutive Securities Excluded from Computation of Diluted Weighted-Average Ordinary Shares Outstanding Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table Text Block] Tax credit carryforwards Tax Credit Carryforward, Amount Domestic Tax Jurisdiction Domestic Tax Jurisdiction [Member] Discontinued R&D program expenses Discontinued Research And Development Expenses Discontinued Research And Development Expenses Less: Imputed interest Lessee, Operating Lease, Liability, Undiscounted Excess Amount Cash and Cash Equivalents [Line Items] Cash and Cash Equivalents [Line Items] Other non-deductible expenses Effective Income Tax Rate Reconciliation, Nondeductible Expense, Other, Percent Exercised (in dollars per share) Share-Based Compensation Arrangements by Share-Based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price Number of square feet to sublease Number of Square Feet to Sublease Number of Square Feet to Sublease ATM Program At-The-Market Program [Member] At-The-Market Program Collaborative Arrangement and Arrangement Other than Collaborative [Table] Collaborative Arrangement and Arrangement Other than Collaborative [Table] Award Timing Disclosures [Line Items] Operating Loss Carryforwards [Line Items] Operating Loss Carryforwards [Line 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sale (in years) Collaborative Arrangement, Rights and Obligations, Period After First Commercial Sale Collaborative Arrangement, Rights and Obligations, Period After First Commercial Sale Maximum aggregate commercial milestone payments Collaborative Arrangement, Rights and Obligations, Maximum Aggregate Commercial Milestone Payments Collaborative Arrangement, Rights and Obligations, Maximum Aggregate Commercial Milestone Payments Other Other Accrued Liabilities, Current Schedule of Effective Income Tax Rate Reconciliation Schedule of Effective Income Tax Rate Reconciliation [Table Text Block] Award vesting period (in years) Share-Based Compensation Arrangement by Share-Based Payment Award, Award Vesting Period Property and equipment, net Property and equipment, net Property, Plant and Equipment, Net State - U.S. State Income Tax Expense (Benefit) [Abstract] State Income Tax Expense (Benefit) Adoption Date Trading Arrangement Adoption Date Reclassifications Reclassification, 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Table [Member] Enhanced UK research and development expenses Effective Income Tax Rate Reconciliation, Nondeductible Expense, Research and Development, Percent Upfront payment Contract with Customer, Liability Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block] Proceeds from maturities of investments in marketable securities Proceeds from Sale and Maturity of Marketable Securities Organization and Description of Business Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block] Unrecognized tax benefits Gross unrecognized tax benefits at beginning of period Gross unrecognized tax benefits at end of period Unrecognized Tax Benefits Proceeds from issuance of debt, net of issuance costs Proceeds from Debt, Net of Issuance Costs Antidilutive securities excluded from computation of diluted weighted-average ordinary shares outstanding (in 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[Axis] Ordinary shares, nominal value (in pound sterling per share) Common Stock, Par or Stated Value Per Share Ordinary shares, shares issued (in shares) Common Stock, Shares, Issued Income tax receivable Income Taxes Receivable, Current Weighted-average remaining lease term Operating Lease, Weighted Average Remaining Lease Term 2029 Long-Term Debt, Maturity, Year Four Granted (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Grants in Period, Gross Additional amount available to borrowers Line Of Credit Facility, Potential Additional Borrowing Capacity Line Of Credit Facility, Potential Additional Borrowing Capacity Use of Estimates Use of Estimates, Policy [Policy Text Block] Entity Public Float Entity Public Float Interest expense Interest expense Interest Expense, Nonoperating Trading Arrangement: Trading Arrangement [Axis] Total Shareholder Return Amount Total Shareholder Return Amount Restricted share awards and units Restricted Share Awards And Units [Member] Restricted Share Awards And Units Maximum number of commercial licenses for worldwide development and commercialization of products Contract With Customer, Maximum Number Of Licenses For Development And Commercialization Of Products Contract With Customer, Maximum Number Of Licenses For Development And Commercialization Of Products Subsequent Event Subsequent Events [Text Block] Insider Trading Arrangements [Line Items] Security Exchange Name Security Exchange Name Forfeited (in dollars per share) Share-Based Compensation Arrangements by Share-Based Payment Award, Options, Forfeitures in Period, Weighted Average Exercise Price Allowance for credit loss Debt Securities, Available-for-Sale, Allowance for Credit Loss, Excluding Accrued Interest Maximum receivable per agreement Contingent Value Rights Agreement, Maximum Receivable Per Agreement Contingent Value Rights Agreement, Maximum Receivable Per Agreement 2027 Lessor, Operating Lease, Payment to be Received, Year 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Investments [Member] Statement [Line Items] Statement [Line Items] Rule 10b5-1 Arrangement Adopted Rule 10b5-1 Arrangement Adopted [Flag] Cash and cash equivalents Cash and Cash Equivalent Counterparty Name [Axis] Counterparty Name [Axis] Subsequent Event [Line Items] Subsequent Event [Line Items] Expenses reflecting development milestone payments Collaborative Arrangement, Rights And Obligations, Aggregate Development Milestone Payment Expense Collaborative Arrangement, Rights And Obligations, Aggregate Development Milestone Payment Expense Ordinary shares Ordinary shares Common Stock [Member] Vested (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Vested in Period Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Non-NEOs Non-NEOs [Member] Corporate debt securities Corporate debt securities, included in: Corporate Debt Securities [Member] Subsidiary, Sale of Stock [Line Items] 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