Revenue from Contracts with Customers - Contract Liabilities (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Dec. 31, 2019
Revenue from Contracts with Customers
Contract liability, Beginning of period	$ 3.9	$ 4.0	$ 4.2	$ 3.9
Deferral	3.0	4.0	6.7	7.9
Revenue recognized	(3.3)	(3.9)	(7.3)	(7.7)
Contract liability, End of period	3.6	4.1	3.6	4.1
Current portion of contract liabilities					$ 3.0	$ 3.6
Non-current portion of contract liabilities					0.6	0.6
Total contract liabilities	$ 3.6	$ 4.1	$ 4.2	$ 4.1	$ 3.6	$ 4.2