Accounts receivable (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Receivables [Abstract]
Revenue recognized in excess of billings on services contracts or unbilled accounts receivable	$ 93.9	$ 87.9
Unearned income	9.0	13.9
Allowance for doubtful accounts	9.5	9.1
Provision for doubtful accounts reported in selling, general and administrative expenses, (income) expense	(0.2)	0.3	$ (0.6)
Long-term receivables	$ 70.3	$ 85.3