Leases and commitments - Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Cash paid for amounts included in the measurement of lease liabilities:
Cash payments for operating leases included in operating activities	$ 31.5	$ 41.0	$ 44.9
Cash payments for finance leases included in financing activities	0.2	1.4	1.9
Cash payments for finance lease included in operating activities	0.0	0.0	$ 0.1
Right-of-use assets obtained in exchange for lease obligations:
Operating leases	$ 14.7	$ 17.2