Employee Incentive Plans - Restricted and Performance Awards (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended				3 Months Ended		9 Months Ended
	Jan. 31, 2021	Jul. 31, 2020	Mar. 31, 2020	Jan. 31, 2020	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Unvested restricted units
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Non-vested, beginning of period (in shares)	5,350,086						5,350,086
Granted (in shares)							3,926,541
Vested (in shares)							(1,234,251)
Forfeited (in shares)							(478,554)
Non-vested, end of period (in shares)					7,563,822		7,563,822
Aggregate intrinsic value, end of period					$ 51.6		$ 51.6
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Non-vested, beginning of period (in dollars per share)	$ 8.45						$ 8.45
Granted (in dollars per share)							3.85
Vested (in dollars per share)							13.01
Forfeited (in dollars per share)							6.11
Non-vested, end of period (in dollars per share)					$ 5.47		$ 5.47
Incentive unit award vesting period							3 years
Units withheld for payroll taxes (in shares)							369,817
Aggregate intrinsic value of units vested					$ 1.5	$ 1.0	$ 5.4	$ 11.9
Fair value of units vested					3.6	$ 6.0	16.1	31.0
Unrecognized compensation cost related to non-vested restricted incentive units					$ 17.7		$ 17.7
Unrecognized compensation costs, weighted average period for recognition							1 year 7 months 6 days
Performance units
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Non-vested, beginning of period (in shares)	2,351,241						2,351,241
Granted (in shares)							1,388,139
Vested (in shares)							(164,553)
Non-vested, end of period (in shares)					3,574,827		3,574,827
Aggregate intrinsic value, end of period					$ 24.4		$ 24.4
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Non-vested, beginning of period (in dollars per share)	$ 8.82						$ 8.82
Granted (in dollars per share)							4.70
Vested (in dollars per share)							26.73
Non-vested, end of period (in dollars per share)					$ 6.40		$ 6.40
Units withheld for payroll taxes (in shares)							63,901
Aggregate intrinsic value of units vested							$ 0.6	0.9
Fair value of units vested							4.4	$ 5.5
Unrecognized compensation cost related to non-vested restricted incentive units					$ 9.7		$ 9.7
Unrecognized compensation costs, weighted average period for recognition							1 year 8 months 12 days
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Grant-date fair value (in dollars per share)	4.70	$ 2.33	$ 1.13	$ 7.69
Beginning TSR Price (in dollars per share)	$ 3.71	$ 2.52	$ 1.25	$ 6.13
Risk-free interest rate	0.17%	0.17%	0.42%	1.62%
Volatility factor	71.00%	67.00%	51.00%	37.00%
Performance units | Minimum
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Percent of units vesting							0.00%
Performance units | Maximum
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Percent of units vesting							200.00%