Consolidated Statement of Stockholders' Equity - 6 months ended Jun. 30, 2018 - USD ($) $ in Thousands	Total	Common Stock Class A	Common Stock Class B	Common Stock Class C	Additional Paid in Capital	Retained Earnings	Accumulated Other Comprehensive Income	Non-controlling Interest
Balance (in shares) at Dec. 31, 2017		35,937,500	173,624,316	42,944,647
Balance at Dec. 31, 2017	$ 742,133	$ 36	$ 174	$ 43	$ 107,008	$ 1,602	$ 31	$ 633,239
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	13,489					1,492		11,997
Distributions to non-controlling interest	(6,048)							(6,048)
Dividends declared	(1,320)
Equity-based compensation expense	20,566				7,566			13,000
Issuance of Class A common stock upon settlement of restricted stock unit awards, net of shares withheld for tax (in shares)		130,000
Issuance of Class A common stock upon settlement of restricted stock unit awards, net of shares withheld for tax	(1,220)	$ 0			(1,220)
Issuance of restricted stock awards (in shares)		61,000
Issuance of restricted stock awards	0
Exchanges of non-controlling interest for Class A common stock (in shares)		13,424,000	(13,424,000)
Exchanges of non-controlling interest for Class A common stock	0	$ 14	$ (14)		37,676			(37,676)
Recognition of tax receivable agreement liability resulting from exchanges of non-controlling interest for Class A common stock	(39,534)				(39,534)
Net deferred tax assets resulting from exchanges of non-controlling interest for Class A common stock	20,349				20,349
Foreign currency translation adjustment	331						48	283
Balance (in shares) at Jun. 30, 2018		49,553,312	160,200,479	42,944,647
Balance at Jun. 30, 2018	$ 748,746	$ 50	$ 160	$ 43	$ 131,845	$ 1,774	$ 79	$ 614,795