Revenue Recognition - Schedule of Disaggregated Revenue by Source (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Net service revenue	$ 147.3	$ 86.9
Net operating fees
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Net service revenue	127.6	70.7
Incentive fees
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Net service revenue	8.0	5.6
Other
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Net service revenue	$ 11.7	$ 10.6