Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Common Stock Common Class A	Common Stock Common Class B	Additional paid-in capital	Retained earnings	Accumulated other comprehensive income (loss), net of tax	Non-controlling interest	Common Class A	Common Class B	Total
Beginning balance, Value at Dec. 31, 2017	$ 2		$ 451,199	$ 7,982	$ 459	$ (414,234)			$ 45,408
Beginning balance, Shares at Dec. 31, 2017	17,696,991	1
Net income				26,883		22,939			49,822
Distributions to non-controlling unitholders						(14,559)			(14,559)
Equity-based compensation expense and dividend equivalents, Value			9,314	(112)					9,202
Equity-based compensation expense and dividend equivalents, Shares	73,462
Dividends to Class A common stockholders				(14,194)					(14,194)
Change in accumulated other comprehensive income					(131)	(122)			(253)
Payroll taxes related to net settled restricted stock units, Value			(895)						(895)
Payroll taxes related to net settled restricted stock units, Shares	(16,037)
Other			483						483
Ending balance, Value at Dec. 31, 2018	$ 2		460,101	20,559	328	(405,976)			75,014
Ending balance, Shares at Dec. 31, 2018	17,754,416	1
Net income				25,040		21,816			46,856
Distributions to non-controlling unitholders						(15,430)			(15,430)
Equity-based compensation expense and dividend equivalents, Value			7,375	(104)					7,271
Equity-based compensation expense and dividend equivalents, Shares	106,390
Dividends to Class A common stockholders				(14,970)					(14,970)
Change in accumulated other comprehensive income					86	80			166
Payroll taxes related to net settled restricted stock units, Value			(1,110)						(1,110)
Payroll taxes related to net settled restricted stock units, Shares	(22,573)
Other			579						579
Ending balance, Value at Dec. 31, 2019	$ 2		466,945	30,525	414	(399,510)			98,376
Ending balance, Shares at Dec. 31, 2019	17,838,233	1					17,838,233	1
Net income				10,964		9,056			20,020
Distributions to non-controlling unitholders						(14,058)			(14,058)
Equity-based compensation expense and dividend equivalents, Value			18,108	(310)					17,798
Equity-based compensation expense and dividend equivalents, Shares	394,701
Dividends to Class A common stockholders				(16,044)					(16,044)
Change in accumulated other comprehensive income					198	18			216
Payroll taxes related to net settled restricted stock units, Value			(2,544)						(2,544)
Payroll taxes related to net settled restricted stock units, Shares	(90,414)
Acquisitions, Value			8,800						8,800
Acquisitions, Shares	248,171
Other			113	4					117
Ending balance, Value at Dec. 31, 2020	$ 2		$ 491,422	$ 25,139	$ 612	$ (404,494)			$ 112,681
Ending balance, Shares at Dec. 31, 2020	18,390,691	1					18,390,691	1