Capitalized contract costs - Summary (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Capitalized Contract Cost [Line Items]
Costs to fulfill a contract - amortization expense	$ 6.7	$ 23.7	$ 27.9
Costs to fulfill a contract	19.2	34.8
Deferred Commissions
Capitalized Contract Cost [Line Items]
Deferred commissions	3.7	4.9
Costs to fulfill a contract - amortization expense	$ 1.5	$ 2.9	$ 2.9