Entity Listings [Table] Entity Listings [Table] Summary of significant accounting policies Significant Accounting Policies [Text Block] Statistical Measurement [Domain] Statistical Measurement [Domain] Contract with customer, contract term Contract with Customer, Contract Term Contract with Customer, Contract Term Award Timing Predetermined Award Timing Predetermined [Flag] Remainder of 2026 Lessee, Operating Lease, Liability, to be Paid, Remainder of Fiscal Year Asset Class [Axis] Asset Class [Axis] Entity File Number Entity File Number Additional Paid-in Capital Additional Paid-in Capital [Member] Tabular List, Table Tabular List [Table Text Block] Recently issued and recently adopted accounting pronouncements New Accounting Pronouncements, Policy [Policy Text Block] Share price at grant date, minimum (in USD per share) Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Grants in Period, Minimum Share Price Grant Date Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Grants in Period, Minimum Share Price Grant Date Increase in accounts payable Increase (Decrease) in Accounts Payable Share options and RSUs Share Options and RSUs [Member] Share Options and RSUs Trading Arrangements, by Individual Trading Arrangements, by Individual [Table] Basic net income per share (in USD per share) Basic net income per share (in USD per share) Earnings Per Share, Basic Adjustment to Compensation: Adjustment to Compensation [Axis] Named Executive Officers, Footnote Named Executive Officers, Footnote [Text Block] Common Stock, capital shares reserved for future issuance (in shares) Common Stock, Capital Shares Reserved for Future Issuance Revenue Revenue from Contract with Customer [Text Block] Other comprehensive (loss) income Other Comprehensive Income (Loss), Net of Tax Schedule of Segment Financial Information Schedule of Segment Reporting Information, by Segment [Table Text Block] Threshold percentage of stock price trigger Debt Instrument, Convertible, Threshold Percentage of Stock Price Trigger Adjustment to Compensation, Amount Adjustment to Compensation Amount Unamortized Debt Issuance Costs Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net Decrease (increase) in other operating assets Increase (Decrease) in Other Operating Assets Share-based compensation expense Share-Based Payment Arrangement, Noncash Expense Employee stock option Share-Based Payment Arrangement, Option [Member] Award Timing MNPI Disclosure Award Timing MNPI Disclosure [Text Block] Antidilutive Securities [Axis] Antidilutive Securities [Axis] Total shareholders' equity Beginning balance Ending balance Equity, Attributable to Parent Measurement Frequency [Axis] Measurement Frequency [Axis] Insider Trading Policies and Procedures [Line Items] Share-based compensation expense Share-Based Payment Arrangement, Expense Current assets Assets, Current [Abstract] Awards forfeited (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Forfeitures in Period Total liabilities and shareholders' equity Liabilities and Equity Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Fair value, recurring Fair Value, Recurring [Member] Number of Share Options Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding [Roll Forward] Liabilities and shareholders’ equity Liabilities and Equity [Abstract] Cover [Abstract] Maximum Maximum [Member] Threshold consecutive trading days Debt Instrument, Convertible, Threshold Consecutive Trading Days Options exercisable, ending balance (in USD per share) Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Exercisable, Weighted Average Exercise Price Reportable segment Reportable Segment [Member] Reportable Segment Accounting Policies [Abstract] Schedule of Maturities of Operating Lease Liabilities Lessee, Operating Lease, Liability, to be Paid, Maturity [Table Text Block] 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] Present value of operating lease liabilities Operating Lease, Liability ADR ADR [Member] Forgone Recovery due to Disqualification of Tax Benefits, Amount Forgone Recovery due to Disqualification of Tax Benefits, Amount Non-Rule 10b5-1 Arrangement Terminated Non-Rule 10b5-1 Arrangement Terminated [Flag] David Berman [Member] David Berman Net income before income taxes Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest Entity Shell Company Entity Shell Company Schedule of Revenue by Major Customers, by Reporting Segments [Table] Schedule of Revenue by Major Customers, by Reporting Segments [Table] Schedule of Long-Term Debt Instruments [Table] Schedule of Long-Term Debt Instruments [Table] Statement of Stockholders' Equity [Abstract] Statement of Cash Flows [Abstract] Company Selected Measure Amount Company Selected Measure Amount 2029 Lessee, Operating Lease, Liability, to be Paid, Year Three Award Timing MNPI Considered Award Timing MNPI Considered [Flag] Total comprehensive income Comprehensive Income (Loss), Net of Tax, Attributable to Parent Awards expired (in USD per share) Share-Based Compensation Arrangements by Share-Based Payment Award, Options, Expirations in Period, Weighted Average Exercise Price Name Measure Name Number of countries KIMMTRAK is approved Number of Countries KIMMTRAK is Approved In number of countries where KIMMTRAK is approved. Schedule of Share-based Compensation Expense Recorded in Consolidated Statements of Operations and Comprehensive Loss Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Table Text Block] Operating lease liabilities, current Operating Lease, Liability, Current Document Fiscal Period Focus Document Fiscal Period Focus Award Timing Method Award Timing Method [Text Block] Award Type [Axis] Award Type [Axis] Percentage of redemption price principal amount Percentage of Redemption Price Principal Amount The Percentage of redemption price equal principal amount of the notes to be redeemed. Deferred revenue, non-current Contract with Customer, Liability, Noncurrent International International [Member] The continent of rest of world for countries. Total assets Assets Trading Symbol Trading Symbol Awards vested (in USD 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 Regulatory Liability [Axis] Regulatory Liability [Axis] Geographical [Domain] Geographical [Domain] Operating Loss Carryforwards [Table] Operating Loss Carryforwards [Table] Equity plan options exercised and units assigned (in shares) Shares Issued, Shares, Share-Based Payment Arrangement, after Forfeiture Accrued expenses and other current liabilities Accrued expenses and other current liabilities Accrued Liabilities and Other Liabilities 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] Other segment (expense) income, net Segment Reporting, Other Segment Item, Amount Net foreign exchange difference on cash held Effect of Exchange Rate on Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Continuing Operation Non-PEO NEO Average Compensation Actually Paid Amount Non-PEO NEO Average Compensation Actually Paid Amount Restricted share unit Restricted Stock Units (RSUs) [Member] Income Statement Location [Domain] Statement of Income Location, Balance [Domain] Compensation Actually Paid vs. Other Measure Compensation Actually Paid vs. Other Measure [Text Block] Entity Emerging Growth Company Entity Emerging Growth Company Deferred shares, par value (in pounds per share) Deferred Stock, Par or Stated Value Per Share Face amount or stated value per share of deferred stock nonredeemable or redeemable solely at the option of the issuer. Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Outstanding, beginning balance (in shares) Outstanding, 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] Insider Trading Policies and Procedures Not Adopted Insider Trading Policies and Procedures Not Adopted [Text Block] Future lease commitments - leases not yet commenced Lease payment Lessee, Operating Lease, Lease Not Yet Commenced, Liability, to be Paid Lessee, Operating Lease, Lease Not Yet Commenced, Liability, to be Paid Convertible number of equity instruments (in shares) Debt Instrument, Convertible, Number of Equity Instruments Percentage of valuation used for redemption Percentage Of Valuation Used For Redemption Percentage Of Valuation Used For Redemption Common stock, shares outstanding (in shares) Beginning balance (in shares) Ending balance (in shares) Common Stock, Shares, Outstanding Plan Name [Axis] Plan Name [Axis] PEO PEO [Member] Interest income Investment Income, Interest Unrealized foreign exchange gains, net Unrealized Gain (Loss), Foreign Currency Transaction, before Tax United States UNITED STATES Changes in assets and liabilities: Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity, Increase (Decrease) in Operating Capital [Abstract] Exercise of share options 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] Medison Medison [Member] The name of entity's collaboration agreements. Accumulated Deficit Retained Earnings [Member] Prepaid expenses and other current assets Prepaid Expense and Other Assets, Current Number of RSUs Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] Entity Address, Postal Zip Code Entity Address, Postal Zip Code Restatement Determination Date Restatement Determination Date Share-Based Payment Arrangement [Abstract] Cash and cash equivalents at beginning of period Cash and cash equivalents at end of period Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Continuing Operation Income Statement [Abstract] Income tax expense Income tax expense Income Tax Expense (Benefit) Revenue, Major Customer [Line Items] Revenue, Major Customer [Line Items] Pension Adjustments Service Cost Pension Adjustments Service Cost [Member] Schedule of Current and Non-current Accruals for Rebates and Chargebacks Accruals for Rebates, Chargebacks and Returns [Table Text Block] Tabular disclosure of accruals for rebates, chargebacks and returns. Subsegments [Axis] Subsegments [Axis] Product and Service [Domain] Product and Service [Domain] Equity incentive plan Equity Incentive Plan [Member] An equity incentive program offers an employee shares of the company they work for. Shares can be awarded through stock options, stocks, warrants, or bonds. Stock options are the most common and recognizable form of employee equity. Coupon interest Interest Expense, Debt, Excluding Amortization Restatement does not require Recovery Restatement Does Not Require Recovery [Text Block] Organization, Consolidation and Presentation of Financial Statements [Abstract] Non-cash lease expense Operating Lease, Right-of-Use Asset, Periodic Reduction Compensation Actually Paid vs. Company Selected Measure Compensation Actually Paid vs. Company Selected Measure [Text Block] Rebates, chargebacks and returns Contract with Customer, Refund Liability, Current Proceeds from exercise of share options 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] Number of authorized shares not disclosed Number Of Authorized Shares Not Disclosed Number Of Authorized Shares Not Disclosed Aggregate non-refundable fee payment Non Refundable Payment Received The amount of the non-refundable payment received. Unvested and outstanding beginning balance (in shares) Unvested and outstanding 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] Cash flows from investing activities Cash Provided by (Used in) Investing Activity, Including Discontinued Operation [Abstract] Unrecognized options compensation cost 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) provided by operating activities Cash Provided by (Used in) Operating Activity, Including Discontinued Operation Schedule of Assumptions Used in Determining Fair Value of Stock Options Schedule of Share-Based Payment Award, Stock Options, Valuation Assumptions [Table Text Block] Selling, general and administrative Selling, General and Administrative Expenses [Member] Equity Valuation Assumption Difference, Footnote Equity Valuation Assumption Difference, Footnote [Text Block] PEO Total Compensation Amount PEO Total Compensation Amount Long-Term Debt, Type [Axis] Long-Term Debt, Type [Axis] Depreciation Depreciation Clinical accruals Clinical Accruals, Current Carrying value as of the balance sheet date of obligations incurred and payable for clinical accruals. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer). Money market funds Money Market Funds [Member] Equity Components [Axis] Equity Components [Axis] Convertible debt Convertible Debt [Member] 2030 and thereafter Lessee, Operating Lease, Liability, to be Paid, After Year Three Lessee, Operating Lease, Liability, to be Paid, After Year Three Description of business Nature of Operations [Text Block] Non-Rule 10b5-1 Arrangement Adopted Non-Rule 10b5-1 Arrangement Adopted [Flag] Number of reportable segments Number of Reportable Segments Awards expired (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Expirations in Period Assumptions for Stock Awards Granted [Abstract] Share-Based Compensation Arrangement by Share-Based Payment Award, Fair Value Assumptions and Methodology [Abstract] Supplemental disclosure of cash flow and noncash information Supplemental Cash Flow Information [Abstract] Revenue from sale of therapies, net Sale of Therapies [Member] Sale of Therapies Entity Address, Country Entity Address, Country Other Performance Measure, Amount Other Performance Measure, Amount R&D expenditure credits Effective Income Tax Rate Reconciliation, Research and Development Expenditure Credits, Percent Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the research and development expenditure credits percent. Weighted Average Exercise Price Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract] Exchange differences on translation of foreign operations Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Gain (Loss) Arising During Period, Net of Tax Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table] Antidilutive Security, Excluded EPS Calculation [Table] Fair value measurements Fair Value Measurement, Policy [Policy Text Block] Total current liabilities Liabilities, Current Other SG&A expenses Other Selling General And Administrative Expenses [Member] Other Selling General And Administrative Expenses (Decrease) increase in cash and cash equivalents Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Period Increase (Decrease), Excluding Exchange Rate Effect, Including Discontinued Operation Individual: Individual [Axis] Research and development Research and Development Expense [Member] Net cash provided by 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] Cash paid for interest Interest Paid, Excluding Capitalized Interest, Operating Activity Document Fiscal Year Focus Document Fiscal Year Focus Basis of presentation Basis of Accounting, Policy [Policy Text Block] Operating lease right of use assets, net Operating Lease, Right-of-Use Asset Forgone Recovery, Explanation of Impracticability Forgone Recovery, Explanation of Impracticability [Text Block] Entity Interactive Data Current Entity Interactive Data Current Plan Name [Domain] Plan Name [Domain] Unrecognized share-based compensation, weighted-average vesting period Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition Exercised of share options (in shares) Awards exercised (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Exercises in Period Options exercisable, aggregate intrinsic value Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Exercisable, Intrinsic Value Segment information Segment Reporting Disclosure [Text Block] 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] Exercise price, minimum (in USD per share) Share-Based Compensation Arrangements By Share Based Payment Award, Options, Grants In Period, Minimum Exercise Price Share-Based Compensation Arrangements By Share Based Payment Award, Options, Grants In Period, Minimum Exercise Price Selling, general and administrative expense SG&A expenses Selling, General and Administrative Expense Other non-current assets Other Assets, Noncurrent Conversion ratio Debt Instrument, Convertible, Conversion Ratio Interest accruals Interest Payable, Current Entity Central Index Key Entity Central Index Key PEO Name PEO Name Conversion price (in USD per share) Debt Instrument, Convertible, Conversion Price 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 Schedule of Segment Reporting Information, by Segment [Table] Schedule of Segment Reporting Information, by Segment [Table] Expected volatility, maximum Share-Based Compensation Arrangement by Share-Based Payment Award, Fair Value Assumptions, Expected Volatility Rate, Maximum Deferred revenue, current Contract with Customer, Liability, Current Segments [Axis] Segments [Axis] Increase in prepayments and other current assets Increase (Decrease) in Prepaid Expense and Other Assets Deferred shares, £0.0001 par value, 5,793,501 shares authorized, issued and outstanding as of March 31, 2026 and December 31, 2025. Deferred Stock Value Aggregate par or stated value of issued nonredeemable deferred stock (or deferred stock redeemable solely at the option of the issuer). Note: elements for number of nonredeemable deferred shares, par value and other disclosure concepts are in another section within stockholders' equity. 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] Additional 402(v) Disclosure Additional 402(v) Disclosure [Text Block] Unrecognized RSU compensation cost Share-Based Payment Arrangement, Nonvested Award, Excluding Option, Cost Not yet Recognized, Amount Europe Europe [Member] Share-based compensation Share-Based Payment Arrangement [Text Block] Assets Assets [Abstract] Underlying Security Market Price Change Underlying Security Market Price Change, Percent Chargebacks Chargeback [Member] Chargebacks for discounts represent the Company's estimated obligations resulting from contractual commitments for specialty distributors to sell KIMMTRAK to qualifying hospitals at a lower price. Debt Instrument [Axis] Debt Instrument [Axis] Awards forfeited (in USD per share) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value Shareholders’ equity Equity, Attributable to Parent [Abstract] 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] Vesting rights percentage Share-Based Compensation Arrangement by Share-Based Payment Award, Award Vesting Rights, Percentage Entity Address, Address Line One Entity Address, Address Line One Entity Address, Address Line Two Entity Address, Address Line Two Research and development expense R&D expenses Research and Development Expense Accumulated Other Comprehensive (Loss) Income AOCI Attributable to Parent [Member] Interest rate on notes Debt Instrument, Interest Rate, Stated Percentage Operating lease liabilities, non-current Operating Lease, Liability, Noncurrent Fair Value as of Grant Date Award Grant Date Fair Value Entity Registrant Name Entity Registrant Name Nature of Expense [Axis] Nature of Expense [Axis] Stock Price or TSR Estimation Method Stock Price or TSR Estimation Method [Text Block] Adjustment for share options and RSUs with dilutive effect (in shares) Incremental Common Shares Attributable to Dilutive Effect of Share-Based Payment Arrangements Awards granted (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period Awards forfeited (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Forfeited in Period Entity Listings [Line Items] Entity Listings [Line Items] Document Quarterly Report Document Quarterly Report Assets at fair value Assets, Fair Value Disclosure Fair Value Long-Term Debt, Fair Value Changed Peer Group, Footnote Changed Peer Group, Footnote [Text Block] Counterparty Name [Domain] Counterparty Name [Domain] 2028 Lessee, Operating Lease, Liability, to be Paid, Year Two Number of operating segments Number of Operating Segments Adjustment To PEO Compensation, Footnote Adjustment To PEO Compensation, Footnote [Text Block] Options outstanding, weighted average remaining contractual term Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term Schedule of Interest-Bearing Loans and Borrowings Schedule of Debt [Table Text Block] Schedule of Accrued Expenses and Other Current Liabilities Schedule of Accounts Payable and Accrued Liabilities [Table Text Block] Awards granted (in USD per share) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value Title Trading Arrangement, Individual Title Peer Group Total Shareholder Return Amount Peer Group Total Shareholder Return Amount Restatement Determination Date: Restatement Determination Date [Axis] Equity plan options exercised and units assigned Shares Issued, Value, Share-Based Payment Arrangement, after Forfeiture Non-PEO NEO Non-PEO NEO [Member] Options outstanding, aggregate intrinsic value Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding, Intrinsic Value Contract manufacturing Accrued Contract Manufacturing Current Carrying value as of the balance sheet date of obligations incurred and payable for Contract manufacturing. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer). Vesting rights (in shares) Share-Based Compensation Arrangement By Share-Based Payment Award, Award Vesting Rights1 Share-Based Compensation Arrangement By Share-Based Payment Award, Award Vesting Rights1 Total interest expense Interest Expense, Debt Name Trading Arrangement, Individual Name Award Type [Domain] Award Type [Domain] 2027 Lessee, Operating Lease, Liability, to be Paid, Year One Equity Awards Adjustments Equity Awards Adjustments [Member] Other Other Noncash Income (Expense) Pension Benefits Adjustments, Footnote Pension Benefits Adjustments, Footnote [Text Block] Compensation Amount Outstanding Recovery Compensation Amount Principal Amount Principal Amount Debt Instrument, Face Amount Subsegments [Domain] Subsegments [Domain] Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Recovery of Erroneously Awarded Compensation Disclosure [Line Items] MNPI Disclosure Timed for Compensation Value MNPI Disclosure Timed for Compensation Value [Flag] Name Awards Close in Time to MNPI Disclosures, Individual Name Accrued expenses and other current liabilities Accounts Payable, Accrued Liabilities, and Other Liabilities Disclosure, Current [Text Block] Weighted average grant date fair value, beginning balance (in USD per share) Weighted average grant date fair value, 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 Aggregate Erroneous Compensation Not Yet Determined Aggregate Erroneous Compensation Not Yet Determined [Text Block] Revenue: Revenues [Abstract] Exercise price, maximum (in USD per share) Share-Based Compensation Arrangements By Share Based Payment Award, Options, Grants In Period, Maximum Exercise Price Share-Based Compensation Arrangements By Share Based Payment Award, Options, Grants In Period, Maximum Exercise Price Accumulated other comprehensive loss Accumulated Other Comprehensive Income (Loss), Net of Tax Country Region Country Region Convertible senior notes Convertible Senior Notes [Member] The 2.5% Convertible Senior Notes were offered in July 2019 and are senior unsecured obligations of the Company. The Notes can be exchanged for a specified number of shares of voting common stock at the option of the issuer or the holder. Segments [Domain] Segments [Domain] Income Statement Location [Axis] Statement of Income Location, Balance [Axis] Aggregate Pension Adjustments Service Cost Aggregate Pension Adjustments Service Cost [Member] Deferred Shares Deferred Shares [Member] Deferred stock that is subordinate to all other stock of the issuer. Inventory, net Inventory, Net Minimum Minimum [Member] Company Selected Measure Name Company Selected Measure Name Non cancellable commitments in relation to development and supply of product Supply Commitment, Remaining Minimum Amount Committed Aggregate Available Trading Arrangement, Securities Aggregate Available Amount Accounts payable Accounts Payable, Current Option to purchase additional notes Debt Instrument, Option to Purchase Maximum Additional Notes Amount of option to purchase maximum additional debt instrument at time of issuance. Stock Appreciation Rights (SARs) Stock Appreciation Rights (SARs) [Member] American depositary shares American Depositary Shares [Member] This member represents American Depositary Shares, each representing one ordinary share, nominal value 0.002 per share. All Executive Categories All Executive Categories [Member] Ordinary shares (voting), £0.002 par value, most recent authority to allot up to a maximum nominal value of £149,633 and shares as of March 31, 2026 and December 31, 2025, respectively, and 50,831,928 and 50,689,271 shares issued and outstanding as of March 31, 2026 and December 31, 2025, respectively. Common Stock, Value, Issued Expected volatility, minimum Share-Based Compensation Arrangement by Share-Based Payment Award, Fair Value Assumptions, Expected Volatility Rate, Minimum Commitments and contingencies Commitments and Contingencies Disclosure [Text Block] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table] Diluted weighted-average number of shares outstanding (in shares) Diluted weighted-average number of shares outstanding (in shares) Weighted Average Number of Shares Outstanding, Diluted Medison and Er-Kim Medison and Er-Kim [Member] Medison and Er-Kim Commitments and contingencies (Note 10) Commitments and Contingencies No Trading Symbol Flag No Trading Symbol Flag Non-GAAP Measure Description Non-GAAP Measure Description [Text Block] Entity Small Business Entity Small Business Schedule of Revenue by Country/Region Based on Location of Customer Revenue from External Customers by Geographic Areas [Table Text Block] Income Tax Disclosure [Abstract] Interest-bearing loans and borrowings Long-Term Debt [Text Block] Document Transition Report Document Transition Report Underlying Securities Award Underlying Securities Amount Deferred tax assets net Deferred Tax Assets, Net Equity Component [Domain] Equity Component [Domain] Document Period End Date Document Period End Date PEO Actually Paid Compensation Amount PEO Actually Paid Compensation Amount Income taxes Income Tax Disclosure [Text Block] United Kingdom UNITED KINGDOM Awards Close in Time to MNPI Disclosures, Table Awards Close in Time to MNPI Disclosures [Table Text Block] Revenue from Contract with Customer [Abstract] Options exercisable, weighted average remaining contractual term Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term (Decrease) increase in operating lease liabilities Increase (Decrease) in Operating Lease Liability Document Type Document Type Basic and diluted net income per share Earnings Per Share [Text Block] Name Outstanding Recovery, Individual Name Authority to allot up to maximum nominal value Common Stock, Authorized to Allot Maximum Nominal Value The maximum amount authorized value of common shares allotted. Additional paid-in capital Additional Paid in Capital Product and Service [Axis] Product and Service [Axis] Total revenue Revenue from sale of therapies, net Revenue from Contract with Customer, Excluding Assessed Tax All Individuals All Individuals [Member] Long-Term Debt, Type [Domain] Long-Term Debt, Type [Domain] Purchase of property and equipment Payments to Acquire Property, Plant, and Equipment Name Forgone Recovery, Individual Name Share-based compensation arrangement by Share-based payment award, expiration period 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] Returns Product returns [Member] The Company estimates the amount of its product sales that may be returned by its customers and records this in the period the related product revenue is recognized. Aggregate Erroneous Compensation Amount Aggregate Erroneous Compensation Amount Peer Group Issuers, Footnote Peer Group Issuers, Footnote [Text Block] Salaries and other employee related cost Salaries And Other Employee Related Cost [Member] Salaries And Other Employee Related Cost Marketable securities Marketable Securities, Current Erroneous Compensation Analysis Erroneous Compensation Analysis [Text Block] As of December 31, 2025 As of March 31, 2026 Contract with Customer, Refund Liability Current liabilities Liabilities, Current [Abstract] Weighted Average Remaining Contractual Term Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Additional Disclosures [Abstract] Geographical [Axis] Geographical [Axis] Rule 10b5-1 Arrangement Terminated Rule 10b5-1 Arrangement Terminated [Flag] Risk free rate, minimum Share-Based Compensation Arrangement by Share-Based Payment Award, Fair Value Assumptions, Risk Free Interest Rate, Minimum Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Line Items] Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Line Items] Foreign currency gains Gain (Loss), Foreign Currency Transaction, before Tax Decrease in accrued expenses Increase (Decrease) in Accrued Liabilities Diluted net income per share (in USD per share) Diluted net income per share (in USD per share) Earnings Per Share, Diluted Erroneously Awarded Compensation Recovery Erroneously Awarded Compensation Recovery [Table] Tebentafusp programs Tebentafusp Programs [Member] Tebentafusp Programs Title of 12(b) Security Title of 12(b) Security Other comprehensive income (loss): Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract] Accruals for Rebates and Chargebacks [Roll Forward] Accruals for Rebates and Chargebacks [Roll Forward] Accruals for Rebates and Chargebacks [Abstract] Deferred stock, shares outstanding (in shares) Deferred Stock, Shares Outstanding Aggregate share number for all nonredeemable deferred stock (or deferred stock redeemable solely at the option of the issuer) held by stockholders. Does not include deferred shares that have been repurchased. Earnings Per Share [Abstract] Share-based compensation expense APIC, Share-Based Payment Arrangement, Option, Increase for Cost Recognition Number of countries KIMMTRAK is commercially launched Number of Countries KIMMTRAK is Commercially Launched Number of Countries KIMMTRAK is Commercially Launched Schedule of Interest Expense Interest Income and Interest Expense Disclosure [Table Text Block] Decrease in deferred revenue Increase (Decrease) in Contract with Customer, Liability Regulatory Liability [Domain] Regulatory Liability [Domain] Less imputed interest Lessee, Operating Lease, Liability, Undiscounted Excess Amount Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] Cash paid for income taxes, net of refunds Income Taxes Paid, Net Awards exercised (in USD per share) Share-Based Compensation Arrangements by Share-Based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price Deferred stock, shares authorized (in shares) Deferred Stock, Shares Authorized The maximum number of nonredeemable deferred shares (or deferred stock redeemable solely at the option of the issuer) permitted to be issued by an entity's charter and bylaws. Award Timing Disclosures [Line Items] Operating Loss Carryforwards [Line Items] Operating Loss Carryforwards [Line Items] Awards granted (in USD per share) Share-Based Compensation Arrangements by Share-Based Payment Award, Options, Grants in Period, Weighted Average Exercise Price Employee related expenses Employee-related Liabilities, Current Measurement Frequency [Domain] Measurement Frequency [Domain] Total lease payments Lessee, Operating Lease, Liability, to be Paid Net income Net income Net income Net Income (Loss) Attributable to Parent Expiration Date Trading Arrangement Expiration Date All other external clinical and preclinical costs Other Clinical And Pre-Clinical Costs [Member] Other Clinical And Pre-Clinical Costs Other accruals Other Accrued Liabilities, Current Vesting period Share-Based Compensation Arrangement by Share-Based Payment Award, Award Vesting Period Property and equipment, net Property, Plant and Equipment, Net Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Abstract] Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Abstract] Segment Reporting Information [Line Items] Segment Reporting Information [Line Items] Adoption Date Trading Arrangement Adoption Date Compensation Actually Paid vs. Net Income Compensation Actually Paid vs. Net Income [Text Block] (Increase) decrease in accounts receivable Increase (Decrease) in Accounts Receivable Entity Current Reporting Status Entity Current Reporting Status Awards Close in Time to MNPI Disclosures Awards Close in Time to MNPI Disclosures [Table] Net proceeds from the offering Proceeds from Convertible Debt Income (Loss) from operations Operating Income (Loss) Accumulated deficit Retained Earnings (Accumulated Deficit) Statement of Financial Position [Abstract] Year-end Fair Value of Equity Awards Granted in Covered Year that are Outstanding and Unvested Year-end Fair Value of Equity Awards Granted in Covered Year that are Outstanding and Unvested [Member] Executive Category: Executive Category [Axis] Interest-bearing loans and borrowings Net Carrying Amount Notes and Loans, Noncurrent Current Fiscal Year End Date Current Fiscal Year End Date Class of Stock [Axis] Class of Stock [Axis] Expected life (years) Share-Based Compensation Arrangement by Share-Based Payment Award, Fair Value Assumptions, Expected Term Aggregate Grant Date Fair Value of Equity Award Amounts Reported in Summary Compensation Table Aggregate Grant Date Fair Value of Equity Award Amounts Reported in Summary Compensation Table [Member] Payables and Accruals [Abstract] 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] Other income, net Other Nonoperating Income (Expense) Statement [Table] Statement [Table] Adjustments for: Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity [Abstract] Cash flows from financing activities Cash Provided by (Used in) Financing Activity, Including Discontinued Operation [Abstract] Fair value (in USD per share) Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value Equity Awards Adjustments, Excluding Value Reported in Compensation Table Equity Awards Adjustments, Excluding Value Reported in the Compensation Table [Member] PRAME programs PRAME Programs [Member] PRAME Programs Proceeds from sale of marketable securities Proceeds from Sale and Maturity of Marketable Securities Antidilutive securities excluded from earnings per share (in shares) Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount All Adjustments to Compensation All Adjustments to Compensation [Member] Amendment Flag Amendment Flag Credits and payments made Credits and Payments Made The amount of credits and payments made. Termination Date Trading Arrangement Termination Date Net cash provided by financing activities Cash Provided by (Used in) Financing Activity, Including Discontinued Operation Insider Trading Policies and Procedures Adopted Insider Trading Policies and Procedures Adopted [Flag] Measure: Measure [Axis] Long-Term Debt, Excluding Current Maturities [Abstract] Long-Term Debt, Excluding Current Maturities [Abstract] Schedule of Number and Weighted Average Exercise Prices of Share Options Activity Share-Based Payment Arrangement, Option, Activity [Table Text Block] Accounts receivable, net Contract with Customer, Receivable, after Allowance for Credit Loss, Current Basic weighted-average number of shares outstanding (in shares) Basic weighted-average number of shares outstanding (in shares) Weighted Average Number of Shares Outstanding, Basic Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Table] Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Table] Schedule of Basic and Diluted Net Income Per Share Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Deferred stock, shares issued (in shares) Deferred Stock, Shares Issued Total number of nonredeemable deferred shares (or deferred stock redeemable solely at the option of the issuer) issued to shareholders (includes related deferred shares that were issued, repurchased, and remain in the treasury). May be all or portion of the number of deferred shares authorized. Excludes preferred shares that are classified as debt. Options exercisable, ending balance (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Exercisable, Number Segment Reporting [Abstract] Cost of revenue from sale of therapies Cost of revenue from sale of therapies Cost of Revenue Pay vs Performance Disclosure, Table Pay vs Performance [Table Text Block] Forgone Recovery due to Violation of Home Country Law, Amount Forgone Recovery due to Violation of Home Country Law, Amount Amortization of debt issuance costs Amortization of Debt Issuance Costs Other income (expense): Nonoperating Income (Expense) [Abstract] Cost and operating expenses: Costs and Expenses [Abstract] Effective tax rate Effective Income Tax Rate Reconciliation, Tax Credit, Percent Number of revenue streams Number of Revenue Streams The number of revenue streams. Outstanding, beginning balance (in USD per share) Outstanding, ending balance (in USD per share) Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding, Weighted Average Exercise Price Forgone Recovery due to Expense of Enforcement, Amount Forgone Recovery due to Expense of Enforcement, Amount External R&D External R&D [Member] External R&D Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items] Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items] Common stock, par value (in pounds per share) Common Stock, Par or Stated Value Per Share Common stock, shares issued (in shares) Common Stock, Shares, Issued Rebates Rebates [Member] Rebates consist of Medicaid and other governmental rebates in the U.S. and other similar programs in Europe. Awards granted (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Grants in Period, Gross Infectious disease programs Infectious Disease Programs [Member] Infectious Disease Programs Share price at grant date, maximum (in USD per share) Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Grants in Period, Maximum Share Price Grant Date Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Grants in Period, Maximum Share Price During Grant Date Use of estimates Use of Estimates, Policy [Policy Text Block] Interest expense Interest Expense, Nonoperating Trading Arrangement: Trading Arrangement [Axis] Total Shareholder Return Amount Total Shareholder Return Amount Insider Trading Arrangements [Line Items] Security Exchange Name Security Exchange Name Awards forfeited (in USD per share) Share-Based Compensation Arrangements by Share-Based Payment Award, Options, Forfeitures in Period, Weighted Average Exercise Price Interim Period, Costs Not Allocable [Domain] Interim Period, Costs Not Allocable [Domain] Total liabilities Liabilities Antidilutive Securities, Name [Domain] Antidilutive Securities, Name [Domain] Unrealized gains on marketable securities Unrealized gains on marketable securities Marketable Security, Unrealized Gain (Loss) Provisions related to sales in the period Provision Related To Sales In The Period The amount of provisions related to sales in the period. Pension Adjustments Prior Service Cost Pension Adjustments Prior Service Cost [Member] Material Terms of Trading Arrangement Material Terms of Trading Arrangement [Text Block] Asset Class [Domain] Asset Class [Domain] Statement [Line Items] Statement [Line Items] Lender fees and issuance costs Unamortized Debt Issuance Expense 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] Schedule of Number and Weighted Average Fair Value of RSUs Awards Share-Based Payment Arrangement, Restricted Stock Unit, Activity [Table Text Block] Threshold trading days Debt Instrument, Convertible, Threshold Trading Days Risk free rate, maximum Share-Based Compensation Arrangement by Share-Based Payment Award, Fair Value Assumptions, Risk Free Interest Rate, Maximum Ordinary Shares Common Stock [Member] Awards 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] Commercial services Accrued Commercial Services Current Carrying value as of the balance sheet date of obligations incurred and payable for commercial services. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).