Income taxes - Changes in Uncertain Tax Positions (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Unrecognized tax benefits:
Amount at beginning of year	$ 3.5	$ 6.4	$ 9.6
Net increase (decrease):
Tax positions taken in current period	0.5	0.7	0.6
Lapse due to applicable statute of limitations	(1.2)	(3.4)	(3.6)
Changes in currency exchange rates		(0.2)	(0.2)
Amount at end of year	$ 2.8	$ 3.5	$ 6.4