Leases - Lease Cost (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Finance lease cost:
Amortization of right-of-use assets	$ 0.3	$ 0.3	$ 0.6	$ 0.6
Interest on lease liabilities	0.0	0.0	0.0	0.1
Net finance lease cost	0.3	0.3	0.6	0.7
Operating lease cost	4.3	3.5	7.8	7.2
Variable lease cost	0.1	0.1	0.2	0.2
Total lease cost	$ 4.7	$ 3.9	$ 8.6	$ 8.1