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								(4,275)	(4,275)
Additional paid-in capital related to tax receivable agreement					11,116				11,116
Other comprehensive income (loss)							(351)		(351)
Stock-based compensation					2,097				2,097
Net income after IPO and Reorganization						$ 16,087		38,215	54,302
Balance at the end of the period at Jun. 30, 2018	$ 265				84,409	16,087	(269)	164,801	265,293
Balance at the end of the period (shares) at Jun. 30, 2018	26,450		48,440
Balance at the beginning of the period at Mar. 31, 2018	$ 265				83,145	3,753	321	139,827	227,311
Balance at the beginning of the period (shares) at Mar. 31, 2018	26,450		48,440
Statement of Stockholders'/Members' Equity
Effect of IPO and Reorganization					1				1
Member distribution after IPO								(4,234)	(4,234)
Other comprehensive income (loss)							(590)		(590)
Stock-based compensation					1,263				1,263
Net income after IPO and Reorganization						12,334		29,208	41,542
Balance at the end of the period at Jun. 30, 2018	$ 265				84,409	16,087	(269)	164,801	265,293
Balance at the end of the period (shares) at Jun. 30, 2018	26,450		48,440
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)
Member distribution after IPO								(3,848)	(3,848)
Effect of Follow-on Offering and CW redemptions	$ 92				48,305		(57)	(48,340)
Effect of Follow-on Offering and CW redemptions (in shares)	9,216		(9,216)
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 income (loss)							(109)	8	(101)
Equity award vestings	$ 2				(4,067)			2,551	(1,514)
Equity award vestings (in shares)	223
Stock-based compensation					3,568				3,568
Net income after IPO and Reorganization						48,215		40,981	89,196
Balance at the end of the period at Jun. 30, 2019	$ 471				193,160	99,898	(498)	161,499	454,530
Balance at the end of the period (shares) at Jun. 30, 2019	47,093		28,020
Balance at the beginning of the period at Mar. 31, 2019	$ 464				189,902	78,490	(259)	147,764	416,361
Balance at the beginning of the period (shares) at Mar. 31, 2019	46,391		28,718
Statement of Stockholders'/Members' Equity
Member distribution after IPO								(3,613)	(3,613)
Effect of Follow-on Offering and CW redemptions	$ 7				4,406		(7)	(4,406)
Effect of Follow-on Offering and CW redemptions (in shares)	698	700	(698)
Adjustment to deferred tax asset from CW Unit redemptions					(1,519)				(1,519)
Additional paid-in capital related to tax receivable agreement					1,072				1,072
Other comprehensive income (loss)							(232)	(139)	(371)
Equity award vestings					(2,593)			2,551	(42)
Equity award vestings (in shares)	4
Stock-based compensation					1,892				1,892
Net income after IPO and Reorganization						21,408		19,342	40,750
Balance at the end of the period at Jun. 30, 2019	$ 471				$ 193,160	$ 99,898	$ (498)	$ 161,499	$ 454,530
Balance at the end of the period (shares) at Jun. 30, 2019	47,093		28,020