Revenue from Contracts with Customers - Deferred Revenue (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Change in Contract with Customer, Liability [Roll Forward]
Opening balance	$ 1.7	$ 2.5
Reclassification of the beginning contract liabilities to revenue, as a result of performance obligation satisfied	(0.6)	(0.5)
Billings in excess of services performed, not recognized as revenue	2.5	3.6
Ending balance	$ 3.6	$ 5.6