Leases - Cash flows (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Leases
Operating cash flows from operating leases	$ 11.8	$ 11.4
Operating cash flows from finance leases	0.2	0.2
Financing cash flows from finance leases	2.1	1.7
Total cash paid for amounts included in the measurement of lease liabilities	14.1	13.3
Finance lease liabilities arising from obtaining right-of-use assets	2.1	1.4
Operating lease liabilities arising from obtaining right-of-use assets	$ 24.7	$ 19.8