Condensed Consolidated Statement of Stockholders' Equity (Deficit) - 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
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, 2017	$ 49,941	6,192	34,332	$ 367	$ 5		90,837
Balance (in shares) at Dec. 31, 2017				36,749,072	50,836,629	1
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
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
Redemption of LLC common units for Class A common stock	1,847		(116)	$ 2			1,733
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		(5,658)					(5,658)
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	(1,542)		1,542
Net income		3,181	14,095	$ 17,276			17,276
Balance at Mar. 31, 2018	$ 52,110	$ 5,025	$ 32,468	$ 369	$ 5		$ 89,977
Balance (in shares) at Mar. 31, 2018				36,930,269	50,706,629	1