Income taxes - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2017
Income Taxes
Cash paid for taxes		$ 0.9	$ 0.8
Domestic Tax Jurisdiction
Income Taxes
Net operating loss (NOL) carryforwards	$ 597.7
Operating loss carryforwards, not subject to expiry				$ 486.6
Domestic Tax Jurisdiction | Research Tax Credit Carryforward
Income Taxes
Increased in unrecognized tax benefits	9.8
Domestic Tax Jurisdiction | Through Tax Year 2037
Income Taxes
Operating loss carryforwards, subject to expiry				$ 111.1
Domestic Tax Jurisdiction | Through Tax Year 2045
Income Taxes
Tax credit carryforwards	13.2
State and Local Jurisdiction
Income Taxes
Net operating loss (NOL) carryforwards	374.4
Operating loss carryforwards, not subject to expiry	26.0
State and Local Jurisdiction | Research Tax Credit Carryforward
Income Taxes
Increased in unrecognized tax benefits	9.8
State and Local Jurisdiction | Through Tax Year 2045
Income Taxes
Operating loss carryforwards, subject to expiry	348.4
State and Local Jurisdiction | Through Tax Year 2040
Income Taxes
Tax credit carryforwards	$ 6.6