Revenue from Contracts with Customers - Contract Liabilities (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Dec. 31, 2019
Revenue from Contracts with Customers
Contract liability, Beginning of period	$ 4.2	$ 3.9
Deferral	3.7	3.9
Revenue recognized	(4.0)	(3.8)
Contract liability, End of period	3.9	4.0
Current portion of contract liabilities			$ 3.3	$ 3.6
Non-current portion of contract liabilities			0.6	0.6
Total contract liabilities	$ 3.9	$ 4.0	$ 3.9	$ 4.2