Equity - Restricted Stock Awards and Restricted Stock Units (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended		6 Months Ended
	Jan. 17, 2018	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Share-based compensation expense			$ 3.6	$ 8.4	$ 6.5
Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Outstanding at beginning of period (in shares)				1,734,535
Granted (in shares)				1,132,770
Vested (in shares)				(590,432)
Forfeited (in shares)				(34,931)
Outstanding at end of period (in shares)		2,241,942		2,241,942
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Outstanding at beginning of period (in dollars per share)				$ 16.97
Granted (in dollars per share)				7.10
Vested (in dollars per share)				17.31
Forfeited (in dollars per share)				15.01
Outstanding at end of period (in dollars per share)		$ 11.92		$ 11.92
Vesting period of awards				5 years
Share-based compensation expense		$ 4.3
Unamortized compensation expense		$ 24.2		$ 24.2
Weighted average remaining vesting period				2 years
Performance Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Outstanding at beginning of period (in shares)				329,277
Granted (in shares)				392,948
Vested (in shares)				0
Forfeited (in shares)				0
Outstanding at end of period (in shares)		722,225		722,225
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Outstanding at beginning of period (in dollars per share)				$ 14.93
Granted (in dollars per share)				9.62
Vested (in dollars per share)				0
Forfeited (in dollars per share)				0
Outstanding at end of period (in dollars per share)		$ 12.04		$ 12.04
Vesting period of awards				3 years
Shares of Class A Common Stock | Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Outstanding at beginning of period (in shares)				268,205
Vested (in shares)				(29,249)
Forfeited (in shares)				(4,387)
Outstanding at end of period (in shares)		234,569		234,569
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Outstanding at beginning of period (in dollars per share)				$ 0
Vested (in dollars per share)				0
Forfeited (in dollars per share)				0
Outstanding at end of period (in dollars per share)		$ 0		$ 0
Shares issued (in shares)	1,258,514