Revenue from Contracts with Customers - Contract Liabilities (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Dec. 31, 2019
Revenue from Contracts with Customers
Contract liability, Beginning of period	$ 3.6	$ 4.1	$ 4.2	$ 3.9
Deferral	3.7	4.1	10.4	12.0
Revenue recognized	(3.3)	(4.0)	(10.6)	(11.7)
Contract liability, End of period	4.0	4.2	4.0	4.2
Current portion of contract liabilities					$ 3.4	$ 3.6
Non-current portion of contract liabilities					0.6	0.6
Total contract liabilities	$ 4.0	$ 4.2	$ 4.2	$ 4.2	$ 4.0	$ 4.2