Other assets - Narratives (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Deferred Costs Capitalized Prepaid And Other Assets Disclosure Abstract
Hosting arrangement service contract implementation cost capitalized	$ 17.9		$ 17.4
Hosting arrangement service contract accumulated amortization	5.7		4.9
Hosting arrangement service contract, net value	12.2		$ 12.5
Hosting arrangement service amortization expense	$ 0.8	$ 0.5