Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Common Class A	Common Class B	Additional paid-in capital	Retained earnings	Accumulated other comprehensive income (loss), net of tax	Non-controlling interest	Total
Beginning balance, Value at Dec. 31, 2019	$ 2		$ 466,945	$ 30,525	$ 414	$ (399,510)	$ 98,376
Beginning balance, Shares at Dec. 31, 2019	17,838,233	1
Net income				2,631		2,659	5,290
Distributions to non-controlling unitholders						(2,777)	(2,777)
Equity-based compensation expense and dividend equivalents, Value			5,962	(289)			5,673
Equity-based compensation expense and dividend equivalents, Shares	368,375
Dividends to Class A common stockholders				(3,986)			(3,986)
Change in accumulated other comprehensive income					(36)	(194)	(230)
Payroll taxes related to net settled restricted stock units, Value			(2,268)				(2,268)
Payroll taxes related to net settled restricted stock units, Shares	(82,645)
Ending balance, Value at Mar. 31, 2020	$ 2		470,639	28,881	378	(399,822)	100,078
Ending balance, Shares at Mar. 31, 2020	18,123,963	1
Beginning balance, Value at Dec. 31, 2019	$ 2		466,945	30,525	414	(399,510)	98,376
Beginning balance, Shares at Dec. 31, 2019	17,838,233	1
Net income							11,214
Change in accumulated other comprehensive income							(113)
Ending balance, Value at Jun. 30, 2020	$ 2		473,451	28,385	440	(400,121)	102,157
Ending balance, Shares at Jun. 30, 2020	18,123,963	1
Beginning balance, Value at Mar. 31, 2020	$ 2		470,639	28,881	378	(399,822)	100,078
Beginning balance, Shares at Mar. 31, 2020	18,123,963	1
Net income				3,489		2,435	5,924
Distributions to non-controlling unitholders						(2,789)	(2,789)
Equity-based compensation expense and dividend equivalents, Value			2,812				2,812
Dividends to Class A common stockholders				(3,987)			(3,987)
Change in accumulated other comprehensive income					62	55	117
Other				2			2
Ending balance, Value at Jun. 30, 2020	$ 2		473,451	28,385	440	(400,121)	102,157
Ending balance, Shares at Jun. 30, 2020	18,123,963	1
Beginning balance, Value at Dec. 31, 2020	$ 2		491,422	25,139	612	(404,494)	112,681
Beginning balance, Shares at Dec. 31, 2020	18,390,691	1
Net income				1,092		548	1,640
Distributions to non-controlling unitholders						(2,889)	(2,889)
Equity-based compensation expense and dividend equivalents, Value			12,679	(472)			12,207
Equity-based compensation expense and dividend equivalents, Shares	459,330
Dividends to Class A common stockholders				(4,326)			(4,326)
Change in accumulated other comprehensive income					41	38	79
Payroll taxes related to net settled restricted stock units, Value			(5,291)				(5,291)
Payroll taxes related to net settled restricted stock units, Shares	(130,773)
Ending balance, Value at Mar. 31, 2021	$ 2		498,810	21,433	653	(406,797)	114,101
Ending balance, Shares at Mar. 31, 2021	18,719,248	1
Beginning balance, Value at Dec. 31, 2020	$ 2		491,422	25,139	612	(404,494)	112,681
Beginning balance, Shares at Dec. 31, 2020	18,390,691	1
Net income							11,886
Change in accumulated other comprehensive income							286
Ending balance, Value at Jun. 30, 2021	$ 2		503,430	22,289	763	(405,765)	120,719
Ending balance, Shares at Jun. 30, 2021	18,719,665	1
Beginning balance, Value at Mar. 31, 2021	$ 2		498,810	21,433	653	(406,797)	114,101
Beginning balance, Shares at Mar. 31, 2021	18,719,248	1
Net income				5,201		5,045	10,246
Distributions to non-controlling unitholders						(4,110)	(4,110)
Equity-based compensation expense and dividend equivalents, Value			4,615				4,615
Equity-based compensation expense and dividend equivalents, Shares	640
Dividends to Class A common stockholders				(4,345)			(4,345)
Change in accumulated other comprehensive income					110	97	207
Payroll taxes related to net settled restricted stock units, Value			(7)				(7)
Payroll taxes related to net settled restricted stock units, Shares	(223)
Other			12				12
Ending balance, Value at Jun. 30, 2021	$ 2		$ 503,430	$ 22,289	$ 763	$ (405,765)	$ 120,719
Ending balance, Shares at Jun. 30, 2021	18,719,665	1