Condensed Consolidated Statement of Stockholders' Equity - USD ($) $ in Thousands	Additional Paid-in Capital	Retained Earnings (Deficit)	Non-controlling Interest	Class A common stock	Class B common stock	Class C common stock	Total
Balance at Dec. 31, 2017	$ 42,520	$ 7,619	$ 21,252	$ 367	$ 5		$ 71,763
Balance (in shares) at Dec. 31, 2017				36,749,000	50,837,000
Increase (Decrease) in Members' Equity (Deficit)
Equity-based compensation	3,218						3,218
Exercise of stock options	137						137
Exercise of stock options (in shares)				6,000
Non-controlling interest adjustment for capital contribution of proceeds from the exercise of stock options	(77)		77
Vesting of restricted stock units (in shares)				2,000
Redemption of LLC common units for Class A common stock	1,848		(115)	$ 2			1,735
Redemption of LLC common units for Class A common stock (in shares)				173,000	(130,000)
Distributions to holders of LLC common units			(19,938)				(19,938)
Dividends		(5,662)					(5,662)
Establishment of liabilities under the Tax Receivable Agreement and related changes to deferred tax assets associated with that liability	(1,414)						(1,414)
Non-controlling interest adjustment	(1,592)		1,592
Net (loss) income		1,821	11,727				13,548
Balance at Mar. 31, 2018	44,640	5,088	17,071	$ 369	$ 5		67,173
Balance (in shares) at Mar. 31, 2018				36,930,000	50,707,000
Increase (Decrease) in Members' Equity (Deficit)
Adoption of accounting standard (see Note 1 - Summary of Significant Accounting Policies) | ASU 2014-09		1,310	2,476				3,786
Balance at Dec. 31, 2018	47,531	(3,370)	(11,621)	$ 372	$ 5		32,917
Balance (in shares) at Dec. 31, 2018				37,192,364	50,706,629	1
Increase (Decrease) in Members' Equity (Deficit)
Equity-based compensation	2,716						2,716
Vesting of restricted stock units (in shares)				1,000
Redemption of LLC common units for Class A common stock	12						12
Redemption of LLC common units for Class A common stock (in shares)				6,000
Distributions to holders of LLC common units			(5,534)				(5,534)
Dividends		(5,699)					(5,699)
Establishment of liabilities under the Tax Receivable Agreement and related changes to deferred tax assets associated with that liability	(8)						(8)
Non-controlling interest adjustment	(1,678)		1,678
Net (loss) income		(19,395)	(7,412)				(26,807)
Balance at Mar. 31, 2019	$ 48,573	(24,759)	(16,557)	$ 372	$ 5		7,634
Balance (in shares) at Mar. 31, 2019				37,198,920	50,706,629	1
Increase (Decrease) in Members' Equity (Deficit)
Adoption of accounting standard (see Note 1 - Summary of Significant Accounting Policies) | ASU 2016-02		$ 3,705	$ 6,332				$ 10,037