Condensed Consolidated Statements of Changes in Equity (Unaudited) - USD ($) $ in Thousands	Total	Additional Paid in Capital	Retained Earnings	Total Stockholders’ Equity	Non-controlling Interest	Shares of Class A Common Stock	Shares of Class A Common Stock Common Stock	Shares of Class B Common Stock	Shares of Class B Common Stock Common Stock
Beginning balance at Dec. 31, 2018	$ 740,814	$ 312,659	$ 119,274	$ 433,069	$ 307,745		$ 684		$ 452
Beginning balance (in shares) at Dec. 31, 2018							68,360,000		45,207,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exchanges of Class B Common Stock for Class A Common Stock (shares)							1,637,000		(1,637,000)
Exchange of Class B Common Stock for Class A Common Stock	0	11,413		11,413	(11,413)		$ 16		$ (16)
Effect of exchange on deferred tax asset, net of liability under tax receivable agreements	896	896		896
$0.05/share of Class A Common Stock Dividend	(3,519)		(3,519)	(3,519)
$0.05/unit distributions to non-controlling unitholders	(2,179)				(2,179)
Other distributions and advance payments to non-controlling interest unitholders	(222)				(222)
Share repurchase (shares)							(1,303,000)
Share repurchases	(17,098)	(13,017)		(13,030)	(4,068)		$ (13)
Stock based compensation expense	2,880	2,880		2,880	0
Vesting of restricted stock units (shares)							50,000
Vesting of restricted stock units	0	136		136	(136)		$ 0
Restricted stock and RSU forfeitures (shares)							0
Restricted Stock and RSU forfeitures	1	0	1	1	0		$ 0
Net income	33,909		18,121	18,121	15,788
Ending balance (in shares) at Mar. 31, 2019							68,744,000		43,570,000
Ending balance at Mar. 31, 2019	755,482	314,967	133,877	449,967	305,515		$ 687		$ 436
Beginning balance at Dec. 31, 2019	781,492	410,596	143,105	554,827	226,665		$ 819		$ 307
Beginning balance (in shares) at Dec. 31, 2019						81,885,384	81,885,000		30,639,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
$0.05/share of Class A Common Stock Dividend	(4,244)		(4,244)	(4,244)
$0.05/unit distributions to non-controlling unitholders	(1,532)				(1,532)
Other distributions and advance payments to non-controlling interest unitholders	(804)				(804)
Stock based compensation expense	4,124	3,001		3,001	1,123
Vesting of restricted stock units (shares)							35,000
Vesting of restricted stock units	0	67		67	(67)		$ 0
Net income	2,417		1,720	1,720	697
Ending balance (in shares) at Mar. 31, 2020						81,920,347	81,920,000	30,638,960	30,639,000
Ending balance at Mar. 31, 2020	$ 781,453	$ 413,664	$ 140,581	$ 555,371	$ 226,082		$ 819		$ 307