Revenue Recognition - Schedule of Disaggregated Revenue by Source (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Disaggregation of Revenue [Line Items]
Net services revenue	$ 314.7	$ 295.0	$ 635.2	$ 570.9
Net operating fees
Disaggregation of Revenue [Line Items]
Net services revenue	287.8	252.9	568.7	494.2
Incentive fees
Disaggregation of Revenue [Line Items]
Net services revenue	1.3	17.4	18.1	29.6
Other
Disaggregation of Revenue [Line Items]
Net services revenue	$ 25.6	$ 24.7	$ 48.4	$ 47.1