Income Taxes - Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Income tax reconciliation, amount
Statutory Tax Rate	$ (22,316)
Changes in Unrecognized Tax Benefits	(10,949)
Total benefit (provision) for income taxes	$ (29,863)	$ (7,041)	$ 30,736
Tax Jurisdiction of Domicile [Extensible Enumeration]	UK
Income tax reconciliation, percent
Statutory income tax rate, percent	25.00%	25.00%
Tax rate difference, percent		(21.60%)	(103.10%)
State taxes net of federal, percent		(2.00%)	(7.90%)
Foreign-Derived Intangible Income ("FDII"), percent		2.20%	13.80%
Uncertain tax positions, percent		(31.90%)
Research and development tax credits, percent		8.90%	13.70%
Share-based compensation, percent		4.80%	(7.40%)
Other Adjustments, percent		(2.60%)	(4.70%)
Changes in valuation allowance, percent		(1657.70%)	(159.80%)
Changes in Unrecognized Tax Benefits, percent	12.30%
IP transfers and allocation		1655.40%	258.60%
Inventory allocation			181.40%
Effective income tax rate	33.50%	(19.50%)	184.60%
UK
Income tax reconciliation, amount
Other	$ 1,152
Income tax reconciliation, percent
Other Adjustments, percent	(1.30%)
United States
Income tax reconciliation, amount
Tax rate difference	$ 714
State and local income taxes	$ 342
Effective Income Tax Rate Reconciliation, State and Local Jurisdiction, Contribution Greater than 50 Percent, Tax Effect [Extensible Enumeration]	stpr:MA
Research and development tax credits	$ 3,509
Share-based compensation	6,569
Other	$ (1,035)
Income tax reconciliation, percent
Tax rate difference, percent	(0.80%)
State taxes net of federal, percent	(0.40%)
Research and development tax credits, percent	(3.90%)
Share-based compensation, percent	(7.40%)
Other Adjustments, percent	1.20%
Switzerland
Income tax reconciliation, amount
Tax rate difference	$ 5,576
State and local income taxes	3,439
Changes in valuation allowance	(10,464)
Enacted changes in tax laws or rates	(7,296)
Other	$ 899
Income tax reconciliation, percent
Tax rate difference, percent	(6.20%)
State taxes net of federal, percent	(3.90%)
Other Adjustments, percent	(1.00%)
Changes in valuation allowance, percent	11.70%
Enacted changes in tax laws or rates, percent	8.20%
Other foreign jurisdictions
Income tax reconciliation, amount
Other	$ (3)

Kiniksa Pharmaceuticals International, plc 10-K