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Income taxes - Additional Information (Details) - USD ($)	3 Months Ended	9 Months Ended	12 Months Ended
	Mar. 31, 2023	Dec. 31, 2023	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Income Taxes [Line Items]
U.K. tax rate	19.00%	25.00%	25.00%	23.50%	19.00%
Tax expense related to current tax			$ 845,000	$ 956,000	$ 688,000
Deferred tax expense			0
Deferred tax liabilities		$ 0	0	0
Upfront cash payment received		81,572,000	52,096,000	81,572,000	87,467,000
SME scheme
Income Taxes [Line Items]
Tax credit		9,900,000	13,200,000	9,900,000	9,700,000
RDEC scheme
Income Taxes [Line Items]
Tax credit		$ 1,100,000	300,000	1,100,000	1,300,000
Collaboration Agreement with Hansoh
Income Taxes [Line Items]
Upfront cash payment received						$ 16,000,000
Upfront payment, tax withholding						$ 1,600,000
Milestone payments received			2,000,000	4,000,000	$ 1,500,000
Milestone payment, tax withholding			$ 200,000	$ 400,000

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Income taxes.

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Amount of obligation to transfer good or service to customer for which consideration has been received or is receivable.

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Amount of current income tax expense (benefit) pertaining to taxable income (loss) from continuing operations.

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Amount of deferred income tax expense (benefit) and income tax credits.

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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The amount of the tax credit carryforward, before tax effects, available to reduce future taxable income under enacted tax laws.

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