Revenue from Contracts with Customers - Contract Liabilities (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Revenue from Contracts with Customers
Contract liability, Beginning of period	$ 3.3	$ 2.7	$ 2.9	$ 2.8
Deferral	3.3	2.2	9.1	6.3
Revenue recognized	(3.2)	(2.2)	(8.6)	(6.4)
Contract liability, End of period	3.4	2.7	3.4	2.7
Current contract liabilities	2.9		2.9		$ 2.4
Non-current contract liabilities	0.5		0.5		0.5
Total contract liabilities	$ 3.4	$ 2.7	$ 3.4	$ 2.7	$ 2.9