CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY Statement - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Treasury Stock	Accumulated Other Comprehensive Income	Retained Earnings	Noncontrolling Interests
Balance, Stockholders Equity at Dec. 31, 2019	$ 641,513	$ 37	$ 645,256	$ (251,241)	$ 15	$ 246,383	$ 1,063
Balance (in shares) at Dec. 31, 2019		36,638,021
Issuance of stock - employee stock purchase plan	2,600		2,600
Issuance of stock - employee stock purchase plan (shares)		16,772
Issuance of stock - 401(k) plan	3,057	$ 0	3,057
Issuance of stock - 401(k) plan (shares)		18,312
Issuance/(cancellation) of non-vested stock	0	$ 0	0
Issuance/(cancellation) of non-vested stock (shares)		166,651
Exercise of stock options	6,070		6,070
Exercise of stock options (in shares)		617,688
Non-cash compensation	19,758		19,758
Surrendered Shares	(54,172)		13,358	(67,530)
Noncontrolling interest distribution	(672)						(672)
Write-off of other comprehensive income	(15)				(15)
Net income	139,604					138,457	1,147
Balance, Stockholders Equity at Sep. 30, 2020	757,743	$ 37	690,099	(318,771)	0	384,840	1,538
Balance (in shares) at Sep. 30, 2020		37,457,444
Balance, Stockholders Equity at Jun. 30, 2020	722,259	$ 37	665,580	(257,625)	0	312,859	1,408
Balance (in shares) at Jun. 30, 2020		36,831,298
Issuance of stock - employee stock purchase plan	914		914
Issuance of stock - employee stock purchase plan (shares)		5,414
Issuance/(cancellation) of non-vested stock	0	$ 0	0
Issuance/(cancellation) of non-vested stock (shares)		81,767
Exercise of stock options	3,123		3,123
Exercise of stock options (in shares)		538,965
Non-cash compensation	7,124		7,124
Surrendered Shares	(47,788)		13,358	(61,146)
Noncontrolling interest distribution	(300)						(300)
Net income	72,411					71,981	430
Balance, Stockholders Equity at Sep. 30, 2020	757,743	$ 37	690,099	(318,771)	0	384,840	1,538
Balance (in shares) at Sep. 30, 2020		37,457,444
Balance, Stockholders Equity at Dec. 31, 2020	810,741	$ 38	698,287	(319,092)	0	429,991	1,517
Balance (in shares) at Dec. 31, 2020		37,470,212
Issuance of stock - employee stock purchase plan	3,022		3,022
Issuance of stock - employee stock purchase plan (shares)		13,357
Issuance/(cancellation) of non-vested stock	0	$ 0	0
Issuance/(cancellation) of non-vested stock (shares)		148,529
Exercise of stock options	1,706		1,706
Exercise of stock options (in shares)		27,186
Non-cash compensation	17,860		17,860
Surrendered Shares	(16,694)			(16,694)
Shares repurchased	(84,879)			(84,879)
Noncontrolling interest distribution	(1,253)						(1,253)
Acquired noncontrolling interest	42,142						42,142
Net income	176,156					175,025	1,131
Balance, Stockholders Equity at Sep. 30, 2021	948,801	$ 38	720,875	(420,665)	0	605,016	43,537
Balance (in shares) at Sep. 30, 2021		37,659,284
Balance, Stockholders Equity at Jun. 30, 2021	875,887	$ 38	714,334	(400,110)	0	560,010	1,615
Balance (in shares) at Jun. 30, 2021		37,553,355
Issuance of stock - employee stock purchase plan	1,061		1,061
Issuance of stock - employee stock purchase plan (shares)		5,095
Issuance/(cancellation) of non-vested stock	0	$ 0	0
Issuance/(cancellation) of non-vested stock (shares)		87,460
Exercise of stock options	1,083		1,083
Exercise of stock options (in shares)		13,374
Non-cash compensation	4,397		4,397
Surrendered Shares	(9,750)			(9,750)
Shares repurchased	(10,805)			(10,805)
Noncontrolling interest distribution	(459)						(459)
Acquired noncontrolling interest	42,142						42,142
Net income	45,245					45,006	239
Balance, Stockholders Equity at Sep. 30, 2021	$ 948,801	$ 38	$ 720,875	$ (420,665)	$ 0	$ 605,016	$ 43,537
Balance (in shares) at Sep. 30, 2021		37,659,284