Condensed Consolidated Statements of Changes in Equity (Deficit) (Unaudited) - USD ($) $ in Thousands	Total	Class A Common Stock	Class B Common Stock	Treasury Stock	Additional Paid-in Capital	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)	Non-Controlling Interests
Beginning Balance at Dec. 31, 2016	$ (8,560)	$ 180			$ 9,145	$ (17,946)	$ 61
Beginning Balance (in shares) at Dec. 31, 2016		18,003,272	271
Redeemable Non-Controlling Interests, Beginning Balance at Dec. 31, 2016	421,976
Net Income	38
Net Income (Loss)	4,891					4,891
Redeemable Non-Controlling Interests, Net Income	(4,853)
Currency Translation Adjustment	1						1
Redeemable Non-Controlling Interests, Currency Translation Adjustment	4
Dividends	(2,849)					(2,849)
Redeemable Non-Controlling Interests, Tax Distributions	(19,125)
Equity-Based Compensation	55,781				55,781
Redeemable Non-Controlling Interests, Equity-Based Compensation	32,598
Forfeiture Liability for Equity Awards	177				177
Net Share Settlement	(4,025)				(4,025)
Redeemable Non-Controlling Interests, Net Share Settlement	(35)
Deliveries of Vested Shares of Common Stock		$ 6			(6)
Deliveries of Vested Shares of Common Stock (in shares)		581,888
Issuance of Shares of Class B Common Stock	(2,789)				(2,789)
Issuance of Shares of Common Stock (in shares)			11
Redeemable Non-Controlling Interests, Issuance of Shares of Class B Common Stock	2,789
Forfeitures of Shares of Class B Common Stock	1,939				1,939
Forfeitures of Shares of Class B Common Stock (in shares)			(3)
Redeemable Non-Controlling Interests, Forfeitures of Shares of Class B Common Stock	(1,939)
Cash-Settled Exchanges of Partnership Units	508				508
Cash-Settled Exchanges of Partnership Units (in shares)			(40)
Redeemable Non-Controlling Interests, Cash-Settled Exchanges of Partnership Units	(39,364)
Adjustment of Redeemable Non-Controlling Interests to Redemption Value	(182,221)				(50,526)	(131,695)
Redeemable Non-Controlling Interests, Adjustment of Redeemable Non-Controlling Interests to Redemption Value	182,221
Ending Balance at Sep. 30, 2017	(137,147)	$ 186			10,204	(147,599)	62
Ending Balance (in shares) at Sep. 30, 2017		18,585,160	239
Redeemable Non-Controlling Interests, Ending Balance at Sep. 30, 2017	574,272
Adoption of Accounting Standard	(6,696)					(6,696)
Beginning Balance at Dec. 31, 2017	422,454	$ 186		$ (2,302)	30,674	(185,991)	155	$ 579,732
Beginning Balance at Dec. 31, 2017	(157,278)
Beginning Balance (in shares) at Dec. 31, 2017		18,599,454	221	(60,333)
Net Income	30,028					19,731		10,297
Net Income (Loss)	19,731
Currency Translation Adjustment	(613)						(305)	(308)
Dividends	(3,154)					(3,154)
Tax Distributions	(15)							(15)
Equity-Based Compensation	90,526				57,250			33,276
Forfeiture Liability for Equity Awards	(545)				(545)
Net Share Settlement	(21,681)				(21,681)
Deliveries of Vested Shares of Common Stock		$ 34			(34)
Deliveries of Vested Shares of Common Stock (in shares)		3,397,147
Issuance of Shares of Class B Common Stock					(6,810)			6,810
Issuance of Shares of Common Stock (in shares)			8
Forfeitures of Shares of Class B Common Stock					678			(678)
Forfeitures of Shares of Class B Common Stock (in shares)			(3)
Cash-Settled Exchanges of Partnership Units	(45,124)				575			(45,699)
Cash-Settled Exchanges of Partnership Units (in shares)			(18)
Treasury Stock Purchases	$ (35,797)			$ (35,797)
Treasury Stock Purchases (in shares)	(665,301)			(665,301)
Ending Balance at Sep. 30, 2018	$ 429,383	$ 220		$ (38,099)	$ 60,107	$ (176,110)	$ (150)	$ 583,415
Ending Balance at Sep. 30, 2018	$ (154,032)
Ending Balance (in shares) at Sep. 30, 2018		21,996,601	208	(725,634)