Fair value measurements - Narrative (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	Sep. 30, 2025	Dec. 31, 2024	Aug. 30, 2024	Aug. 07, 2020
Debt Instrument [Line Items]
Warrant liability	$ 14.4	$ 16.2
Senior Unsecured Notes Due August 2028 | Senior Notes
Debt Instrument [Line Items]
Stated interest rate percentage	3.875%	3.875%		3.875%
Long-term debt, fair value	$ 368.6	$ 369.1
Series I Warrants
Debt Instrument [Line Items]
Class of warrant or right, number of securities called by warrants or rights (in shares)			1.0
Exercise price per share (in dollars per share)			$ 9.8802
Series II Warrants
Debt Instrument [Line Items]
Class of warrant or right, number of securities called by warrants or rights (in shares)			1.5
Exercise price per share (in dollars per share)			$ 15.7185