CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY - USD ($) $ in Thousands	Class A Common Stock Conversion of Class A-2 to Class A	Class A Common Stock Conversion of Class B to Class A	Class A Common Stock	Class A-2 Common Stock Conversion of Class A-2 to Class A	Class A-2 Common Stock	Class B Common Stock Conversion of Class B to Class A	Class B Common Stock	Conversion of Class B to Class A Total Stockholders' Equity	Conversion of Class B to Class A Additional Paid-In Capital	Conversion of Class B to Class A Noncontrolling Interests	Total Stockholders' Equity	Additional Paid-In Capital	Retained Earnings (Accumulated Deficit)	Accumulated Other Comprehensive Income (Loss)	Noncontrolling Interests	Total
Beginning balance at Dec. 31, 2017			$ 592		$ 67		$ 404				$ 656,647	$ 673,141	$ (17,859)	$ 302	$ 406,722	$ 1,063,369
Beginning balance (in shares) at Dec. 31, 2017			59,182,176		6,731,845		40,331,989
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Conversion of common stock	$ 67	$ 144		$ (67)		$ (144)		$ 146,865	$ 146,865	$ (146,865)
Conversion of common stock (in shares)	6,731,839	14,305,146		(6,731,839)		(14,305,146)
ESPP shares issued											99	99			(13)	86
ESPP shares issued (in shares)			6,413
Equity-based compensation											5,543	5,543			2,487	8,030
Issuance of restricted shares			$ 4								2,325	2,321			(2,325)
Issuance of restricted shares (in shares)			438,182
Exercise of restricted stock units											104	104			(104)
Exercise of restricted stock units (in shares)			27,860
Stock options exercised			$ 1								1,019	1,018			(374)	645
Stock options exercised (in shares)			79,333
Repurchase of common stock			$ (1)								(804)	(803)			(73)	(877)
Repurchase of common stock ( in shares)			(62,777)		(6)
Restricted shares forfeited											(380)	(380)			379	(1)
Restricted shares forfeited (in shares)			(49,638)
Distributions to noncontrolling interests, net															(506)	(506)
NCI income tax adjustment											(229)	(229)			229
Foreign currency translation adjustment											(319)			(319)	(176)	(495)
Net income											50,012		50,012		22,409	72,421
Ending balance at Sep. 30, 2018			$ 807				$ 260				861,340	828,137	32,153	(17)	281,332	1,142,672
Ending balance (in shares) at Sep. 30, 2018			80,658,534				26,026,843
Beginning balance at Jun. 30, 2018			$ 773				$ 294				800,820	790,699	9,202	(148)	307,991	1,108,811
Beginning balance (in shares) at Jun. 30, 2018			77,298,660				29,383,320
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Conversion of common stock		$ 34				$ (34)		35,062	35,062	(35,062)
Conversion of common stock (in shares)		3,356,477				(3,356,477)
ESPP shares issued											49	49			(17)	32
ESPP shares issued (in shares)			2,427
Equity-based compensation											1,926	1,926			639	2,565
Issuance of restricted shares											60	60			(60)
Issuance of restricted shares (in shares)			7,587
Stock options exercised											643	642			(375)	268
Stock options exercised (in shares)			42,124
Repurchase of common stock											(221)	(220)			1	(220)
Repurchase of common stock ( in shares)			(17,743)
Restricted shares forfeited											(310)	(310)			309	(1)
Restricted shares forfeited (in shares)			(30,998)
Distributions to noncontrolling interests, net															(226)	(226)
NCI income tax adjustment											229	229			(229)
Foreign currency translation adjustment											131			131	45	176
Net income											22,951		22,951		8,316	31,267
Ending balance at Sep. 30, 2018			$ 807				$ 260				861,340	828,137	32,153	(17)	281,332	1,142,672
Ending balance (in shares) at Sep. 30, 2018			80,658,534				26,026,843
Beginning balance at Dec. 31, 2018			$ 790				$ 260				832,934	813,599	18,653	(368)	277,839	$ 1,110,773
Beginning balance (in shares) at Dec. 31, 2018			78,956,555				26,026,843
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Conversion of common stock		$ 75				$ (75)		82,706	82,706	(82,706)
Conversion of common stock (in shares)		7,564,868				(7,564,868)										7,564,868
ESPP shares issued											79	79			1	$ 80
ESPP shares issued (in shares)			8,746
Equity-based compensation											9,045	9,045			2,829	11,874
Issuance of restricted shares			$ 14								3,604	3,590			(3,604)
Issuance of restricted shares (in shares)			1,391,479
Exercise of restricted stock units											4	4			(4)
Exercise of restricted stock units (in shares)			1,250
Stock options exercised											84	84			(54)	30
Stock options exercised (in shares)			5,282
Repurchase of common stock			$ (16)								(15,902)	(15,886)			2,501	(13,401)
Repurchase of common stock ( in shares)			(1,597,150)
Restricted shares forfeited											(36)	(36)			36
Restricted shares forfeited (in shares)			(10,017)
Distributions to noncontrolling interests, net															(349)	(349)
NCI income tax adjustment											(89)	(89)			89
Foreign currency translation adjustment											387	19		368	85	472
Net income											12,714		12,714		3,926	16,640
Ending balance at Sep. 30, 2019			$ 863				$ 185				925,708	893,293	31,367		200,411	1,126,119
Ending balance (in shares) at Sep. 30, 2019			86,321,013				18,461,975
Beginning balance at Jun. 30, 2019			$ 802				$ 260				848,638	821,968	25,988	(380)	278,210	$ 1,126,848
Beginning balance (in shares) at Jun. 30, 2019			80,176,078				26,026,843
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Conversion of common stock		$ 75				$ (75)		$ 82,706	$ 82,706	$ (82,706)
Conversion of common stock (in shares)		7,564,868				(7,564,868)										7,564,868
ESPP shares issued											21	21			3	$ 24
ESPP shares issued (in shares)			3,079
Equity-based compensation											2,774	2,774			792	3,566
Issuance of restricted shares											41	41			(41)
Issuance of restricted shares (in shares)			17,549
Stock options exercised											84	84			(54)	30
Stock options exercised (in shares)			5,282
Repurchase of common stock			$ (14)								(14,361)	(14,347)			2,476	(11,885)
Repurchase of common stock ( in shares)			(1,444,648)
Restricted shares forfeited											(13)	(13)			13
Restricted shares forfeited (in shares)			(1,195)
Distributions to noncontrolling interests, net															(124)	(124)
NCI income tax adjustment											(40)	(40)			40
Foreign currency translation adjustment											399	19		$ 380	89	488
Net income											5,379		5,379		1,793	7,172
Ending balance at Sep. 30, 2019			$ 863				$ 185				$ 925,708	$ 893,293	$ 31,367		$ 200,411	$ 1,126,119
Ending balance (in shares) at Sep. 30, 2019			86,321,013				18,461,975