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
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	10,535						10,535
Exercise of stock options	149						149
Exercise of stock options (in shares)				7,000
Non-controlling interest adjustment for capital contribution of proceeds from the exercise of stock options	(86)		86
Vesting of restricted stock units	73		(74)	$ 1
Vesting of restricted stock units (in shares)				89,000
Repurchases of Class A common stock for withholding taxes on vested RSUs	(62)						(62)
Repurchases of Class A common stock for withholding taxes on vested RSUs (in shares)				(3,000)
Disgorgement of short-swing profits by Section 16 officer	557						557
Redemption of LLC common units for Class A common stock	4,332		(153)	$ 3			4,182
Redemption of LLC common units for Class A common stock (in shares)				215,000	(130,000)
Distributions to holders of LLC common units			(98,347)				(98,347)
Dividends		(17,000)					(17,000)
Establishment of liabilities under the Tax Receivable Agreement and related changes to deferred tax assets associated with that liability	(3,085)						(3,085)
Non-controlling interest adjustment	(12,184)		12,184
Net income		45,228	101,772	$ 147,000			147,000
Balance at Sep. 30, 2018	$ 50,170	$ 35,730	$ 52,276	$ 371	$ 5		$ 138,552
Balance (in shares) at Sep. 30, 2018				37,056,971	50,706,629	1