Stock-based Payments - Summary of RSU Compensation Expense (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Pre-IPO stock-based compensation	$ 5.9	$ 10.6	$ 12.2	$ 22.2
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Pre-IPO stock-based compensation	12.7	12.0	24.4	22.0
Unrecognized compensation expense related to RSUs	69.9		69.9
Co-Investment RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Pre-IPO stock-based compensation	0.0	0.1	0.1	0.2
Unrecognized compensation expense related to RSUs	0.0		0.0
Time-Based RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Pre-IPO stock-based compensation	11.4	11.4	22.2	21.1
Unrecognized compensation expense related to RSUs	58.1		58.1
Performance-Based RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Pre-IPO stock-based compensation	1.3	$ 0.5	2.1	$ 0.7
Unrecognized compensation expense related to RSUs	$ 11.8		$ 11.8