Condensed Consolidated Statements of Changes in Equity - USD ($) $ in Thousands	Total	Class A Common Stock	Class B Common Stock	Treasury Stock	Additional Paid-In Capital	Retained Earnings (Accumulated Deficit)	Accumulated Other Comprehensive Income (Loss)	Noncontrolling Interests
Balance at beginning of the period at Dec. 31, 2016	$ 251,441	$ 210	$ 311	$ (10,930)	$ 291,026	$ (68,229)	$ (543)	$ 39,596
Balance at beginning of the period (in shares) at Dec. 31, 2016		20,948,998	31,138,193	(387,890)
Cumulative Effect Adjustment upon Adoption of ASU (ASU 2016-09) at Dec. 31, 2016	658				4,855	(4,197)
Balance at beginning of the period, as adjusted at Dec. 31, 2016	252,099	$ 210	$ 311	$ (10,930)	295,881	(72,426)	(543)	39,596
Changes in Equity
Net income (loss)	132,174					54,213		77,961
Equity-based compensation	72,912	$ 16			71,228			1,668
Equity-based compensation (in shares)		1,602,236
Other comprehensive income (loss)	2,234						1,086	1,148
Dividends declared and distributions	(164,218)				20,911	(80,923)		(104,206)
Treasury Stock Purchases	$ (9,832)			$ (9,832)
Treasury Stock purchases (in shares)	(264,710)			(264,710)
Exercise of Stock options	$ 5,571	$ 2			5,569
Exercise of stock options (in shares)		256,270
Issuance of Class A common stock and cancellation of Class B common stock in connection with offerings and other exchanges	52,011	$ 111	$ (111)		57,035			(5,024)
Issuance of Class A common stock and cancellation of Class B common stock in connection with offerings and other exchanges (in shares)		11,092,457	(11,092,457)
Equity-based payments to non-employees	4,066				4,066
Other	55				55
Other (in shares)		(86)
Balance at end of the period at Sep. 30, 2017	347,072	$ 339	$ 200	$ (20,762)	454,745	(99,136)	543	11,143
Balance at end of the period (in shares) at Sep. 30, 2017		33,899,875	20,045,736	(652,600)
Balance at beginning of the period at Dec. 31, 2016	251,441	$ 210	$ 311	$ (10,930)	291,026	(68,229)	(543)	39,596
Balance at beginning of the period (in shares) at Dec. 31, 2016		20,948,998	31,138,193	(387,890)
Cumulative Effect Adjustment upon Adoption of ASU (ASU 2016-09) at Dec. 31, 2016	658				4,855	(4,197)
Balance at beginning of the period, as adjusted at Dec. 31, 2016	252,099	$ 210	$ 311	$ (10,930)	295,881	(72,426)	(543)	39,596
Changes in Equity
Other comprehensive income (loss) | ASU 2016-01	317
Balance at end of the period at Dec. 31, 2017	344,256	$ 342	$ 199	$ (23,188)	487,163	(139,918)	352	19,306
Balance at end of the period (in shares) at Dec. 31, 2017		34,163,042	19,912,230	(707,416)
Cumulative Effect Adjustment upon Adoption of ASU (ASU 2014-09) at Dec. 31, 2017	3,155					3,155
Cumulative Effect Adjustment upon Adoption of ASU (ASU 2016-01) at Dec. 31, 2017						(317)	317
Balance at beginning of the period, as adjusted at Dec. 31, 2017	347,411	$ 342	$ 199	$ (23,188)	487,163	(137,080)	669	19,306
Changes in Equity
Net income (loss)	151,999					101,464		50,535
Equity-based compensation	88,776	$ 30			87,812			934
Equity-based compensation (in shares)		3,004,647
Other comprehensive income (loss)	(871)						(703)	(168)
Dividends declared and distributions	(286,145)				44,727	(214,978)		(115,894)
Treasury Stock Purchases	$ (24,692)			$ (24,692)
Treasury Stock purchases (in shares)	(484,061)			(484,061)
Exercise of Stock options	$ 6,781	$ 3			6,778
Exercise of stock options (in shares)		348,280
Issuance of Class A common stock and cancellation of Class B common stock in connection with offerings and other exchanges	39,694	$ 94	$ (94)		37,257			2,437
Issuance of Class A common stock and cancellation of Class B common stock in connection with offerings and other exchanges (in shares)		9,392,754	(9,392,754)
Equity-based payments to non-employees	4,669				4,669
Other	(677)							(677)
Other (in shares)			(26,118)
Balance at end of the period at Sep. 30, 2018	$ 326,945	$ 469	$ 105	$ (47,880)	$ 668,406	$ (250,594)	$ (34)	$ (43,527)
Balance at end of the period (in shares) at Sep. 30, 2018		46,908,723	10,493,358	(1,191,477)