CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS’ EQUITY - USD ($) shares in Thousands, $ in Thousands	Class A Common Stock Common stock	Class A Common Stock	Class B Common Stock Common stock	Members' Equity (Deficit)	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Non-controlling Interest	Total
Balance at the beginning of the period at Dec. 31, 2017				$ (36,299)			$ 82		$ (36,217)
Statement of Stockholders'/Members' Equity
Member distributions prior to IPO				(26,000)					(26,000)
Net income prior to IPO				13,648					13,648
Effect of IPO and Reorganization	$ 265			$ 48,651	$ 71,196			$ 130,861	250,973
Effect of IPO and Reorganization (shares)	26,450		48,440
Member distribution after IPO								(5,848)	(5,848)
Effect of Follow-on Offering	$ 112				24,472			(25,293)	(709)
Effect of Follow-on Offering (in shares)	11,197		(11,197)
Additional paid-in capital related to tax receivable agreement					28,552				28,552
Other comprehensive loss							(870)		(870)
Stock-based compensation					3,384				3,384
Net income						$ 34,759		63,191	97,950
Balance at the end of the period at Sep. 30, 2018	$ 377				127,604	34,759	(788)	162,911	324,863
Balance at the end of the period (shares) at Sep. 30, 2018	37,647		37,243
Balance at the beginning of the period at Jun. 30, 2018	$ 265				84,409	16,087	(269)	164,801	265,293
Balance at the beginning of the period (shares) at Jun. 30, 2018	26,450		48,440
Statement of Stockholders'/Members' Equity
Member distribution after IPO								(1,573)	(1,573)
Effect of Follow-on Offering	$ 112				24,472			(25,293)	(709)
Effect of Follow-on Offering (in shares)	11,197		(11,197)
Additional paid-in capital related to tax receivable agreement					17,436				17,436
Other comprehensive loss							(519)		(519)
Stock-based compensation					1,287				1,287
Net income						18,672		24,976	43,648
Balance at the end of the period at Sep. 30, 2018	$ 377				127,604	34,759	(788)	162,911	324,863
Balance at the end of the period (shares) at Sep. 30, 2018	37,647		37,243
Balance at the beginning of the period at Dec. 31, 2018	$ 377				126,418	51,683	(820)	184,670	362,328
Balance at the beginning of the period (shares) at Dec. 31, 2018	37,654		37,236
Statement of Stockholders'/Members' Equity
Correction to equity reclassification related to prior equity offering					14,035		488	(14,523)
Adjustments to prior periods					(1,466)			960	(506)
Member distribution after IPO								(5,853)	(5,853)
Effect of CW Unit redemptions	$ 92				48,344		(57)	(48,379)
Effect of CW Unit redemptions (in shares)	9,221		(9,221)
Effect of Follow-on Offering (in shares)		700
Adjustment to deferred tax asset from CW Unit redemptions					(9,751)				(9,751)
Additional paid-in capital related to tax receivable agreement					14,652				14,652
Other comprehensive loss							(403)	(167)	(570)
Equity award vestings	$ 2				(4,080)			2,551	(1,527)
Equity award vestings (in shares)	225
Stock-based compensation					5,257				5,257
Net income						67,554		57,475	125,029
Balance at the end of the period at Sep. 30, 2019	$ 471				193,409	119,237	(792)	176,734	489,059
Balance at the end of the period (shares) at Sep. 30, 2019	47,100		28,015
Balance at the beginning of the period at Jun. 30, 2019	$ 471				193,160	99,898	(498)	161,499	454,530
Balance at the beginning of the period (shares) at Jun. 30, 2019	47,093		28,020
Statement of Stockholders'/Members' Equity
Adjustments to prior periods					(1,466)			960	(506)
Member distribution after IPO								(2,005)	(2,005)
Effect of CW Unit redemptions					39			(39)
Effect of CW Unit redemptions (in shares)	5		(5)
Other comprehensive loss							(294)	(175)	(469)
Equity award vestings					(13)				(13)
Equity award vestings (in shares)	2
Stock-based compensation					1,689				1,689
Net income						19,339		16,494	35,833
Balance at the end of the period at Sep. 30, 2019	$ 471				$ 193,409	$ 119,237	$ (792)	$ 176,734	$ 489,059
Balance at the end of the period (shares) at Sep. 30, 2019	47,100		28,015