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)	88,903					35,008		53,895
Equity-based compensation	49,729	$ 16			48,514			1,199
Equity-based compensation (in shares)		1,554,754
Other comprehensive income (loss)	1,282						617	665
Dividends declared and distributions	(143,138)				17,176	(64,872)		(95,442)
Treasury Stock Purchases	$ (9,266)			$ (9,266)
Treasury Stock purchases (in shares)	(250,550)			(250,550)
Class A Partnership Units and other equity purchased or converted into Class A Common Stock	$ 6,673	$ 3	$ (1)		6,685			(14)
Class A Partnership units and other equity purchased or converted into Class A Common Stock (in shares)		297,755	(54,678)
Issuance of Class A common stock and cancellation of Class B common stock in connection with offerings and other exchanges	22,080	$ 53	$ (53)		28,374			(6,294)
Issuance of Class A common stock and cancellation of Class B common stock in connection with offerings and other exchanges (in shares)		5,356,876	(5,356,876)
Equity-based payments to non-employees	2,914				2,914
Other	(36)				(36)
Balance at end of the period at Jun. 30, 2017	271,240	$ 282	$ 257	$ (20,196)	399,508	(102,290)	74	(6,395)
Balance at end of the period (in shares) at Jun. 30, 2017		28,158,383	25,726,639	(638,440)
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)	107,111					69,015		38,096
Equity-based compensation	58,335	$ 30			57,603			702
Equity-based compensation (in shares)		2,962,076
Other comprehensive income (loss)	(164)						(212)	48
Dividends declared and distributions	(167,145)				24,767	(114,191)		(77,721)
Treasury Stock Purchases	$ (24,172)			$ (24,172)
Treasury Stock purchases (in shares)	(475,169)			(475,169)
Exercise of Stock options	$ 6,695	$ 3			6,692
Exercise of stock options (in shares)		343,780
Issuance of Class A common stock and cancellation of Class B common stock in connection with offerings and other exchanges	22,039	$ 47	$ (47)		25,994			(3,955)
Issuance of Class A common stock and cancellation of Class B common stock in connection with offerings and other exchanges (in shares)		4,707,537	(4,707,537)
Equity-based payments to non-employees	3,678				3,678
Other	(677)		$ (26,118)					(677)
Balance at end of the period at Jun. 30, 2018	$ 353,111	$ 422	$ 152	$ (47,360)	$ 605,897	$ (182,256)	$ 457	$ (24,201)
Balance at end of the period (in shares) at Jun. 30, 2018		42,176,435	15,178,575	(1,182,585)