Stock-Based Compensation Plans and Employee Benefits (Performance Incentive Plans) (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($) ownership_class $ / shares shares	Dec. 31, 2019 USD ($) $ / shares shares	Dec. 31, 2018 USD ($)	May 01, 2019 shares	Apr. 30, 2019 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting rights percentage	15.00%
Equity-based compensation | $	$ 39,354	$ 30,436	$ 17,563
Performance Incentive Plan
Accrued expenses | $	$ 94,724	83,778
Long-term Incentive Plan 2009
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Ownership percentage of class A units	100.00%
Performance Incentive Plan
Number of shares authorized for issuance (in shares)				8,900,000	8,000,000.0
Shares available for grant (in shares)	2,400,000
iPIP Plans
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	6 years
Vesting rights percentage	40.00%
Performance Incentive Plan
Accrued expenses | $	$ 69,100	$ 41,900
2013-2014 Performance Incentive Plan
Performance Incentive Plan
Points at beginning of period (in shares)	81.17
Forfeited (in shares)	(1.00)
Points at end of period (in shares)	80.17	81.17
iPIP distributions to plan participants | $		$ 7,400
iPIP distributions, equity component (in shares)		389,545
iPIP distributions, equity component, fair value (in dollars per share) | $ / shares		$ 9.21
iPIP distributions, shares issued net of tax withholdings (in shares)		209,118
2019-2020 Performance Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of ownership classes of consolidated subsidiary | ownership_class	2
Equity-based compensation | $	$ 3,400	$ 2,900
Settlement or distribution on units and awards, cash	50.00%
Settlement or distribution on units and awards, common stock	50.00%
2015-2016 Performance Incentive Plan
Performance Incentive Plan
Points at beginning of period (in shares)	73.28
Forfeited (in shares)	(2.88)
Points at end of period (in shares)	70.40	73.28
iPIP distributions to plan participants | $	$ 1,500	$ 9,400
iPIP distributions, equity component (in shares)	54,245	356,065
iPIP distributions, equity component, fair value (in dollars per share) | $ / shares	$ 14.51	$ 13.11
iPIP distributions, shares issued net of tax withholdings (in shares)	32,825	192,829
2017-2018 Performance Incentive Plan
Performance Incentive Plan
Points at beginning of period (in shares)	77.27
Forfeited (in shares)	(3.93)
Points at end of period (in shares)	73.34	77.27
2013-2018 Performance Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity-based compensation | $	$ 30,700	$ 21,200	$ 15,000
Settlement or distribution on units and awards, cash	50.00%
Settlement or distribution on units and awards, common stock	50.00%