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, 2018	$ 482,633	$ 36	$ 603,666	$ (241,685)	$ 15	$ 119,550	$ 1,051
Balance (in shares) at Dec. 31, 2018		36,252,280
Issuance of stock - employee stock purchase plan	1,534		1,534
Issuance of stock - employee stock purchase plan (shares)		15,037
Issuance of stock - 401(k) plan	4,613		4,613
Issuance of stock - 401(k) plan (shares)		38,402
Issuance/(cancellation) of non-vested stock	0	$ 0	0
Issuance/(cancellation) of non-vested stock (shares)		97,181
Exercise of stock options	1,343		1,343
Exercise of stock options (in shares)		42,691
Non-cash compensation	12,153		12,153
Surrendered Shares	(4,490)			(4,490)
Noncontrolling interest distribution	(457)						(457)
Net income	65,613					65,046	567
Balance, Stockholders Equity at Jun. 30, 2019	562,942	$ 36	623,309	(246,175)	15	184,596	1,161
Balance (in shares) at Jun. 30, 2019		36,445,591
Balance, Stockholders Equity at Mar. 31, 2019	521,200	$ 36	613,714	(244,373)	15	150,854	954
Balance (in shares) at Mar. 31, 2019		36,337,743
Issuance of stock - employee stock purchase plan	752		752
Issuance of stock - employee stock purchase plan (shares)		7,181
Issuance of stock - 401(k) plan	2,318		2,318
Issuance of stock - 401(k) plan (shares)		18,811
Issuance/(cancellation) of non-vested stock	0	$ 0	0
Issuance/(cancellation) of non-vested stock (shares)		46,019
Exercise of stock options	987		987
Exercise of stock options (in shares)		35,837
Non-cash compensation	5,538		5,538
Surrendered Shares	(1,802)			(1,802)
Noncontrolling interest distribution	(91)						(91)
Net income	34,040					33,742	298
Balance, Stockholders Equity at Jun. 30, 2019	562,942	$ 36	623,309	(246,175)	15	184,596	1,161
Balance (in shares) at Jun. 30, 2019		36,445,591
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	1,686		1,686
Issuance of stock - employee stock purchase plan (shares)		11,358
Issuance of stock - 401(k) plan	3,057		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)		84,884
Exercise of stock options	2,947		2,947
Exercise of stock options (in shares)		78,723
Non-cash compensation	12,634		12,634
Surrendered Shares	(6,384)			(6,384)
Noncontrolling interest distribution	(372)						(372)
Write-off of other comprehensive income	(15)				(15)
Net income	67,193					66,476	717
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
Balance, Stockholders Equity at Mar. 31, 2020	680,144	$ 37	656,266	(255,291)	0	278,185	947
Balance (in shares) at Mar. 31, 2020		36,746,554
Issuance of stock - employee stock purchase plan	826		826
Issuance of stock - employee stock purchase plan (shares)		5,295
Issuance/(cancellation) of non-vested stock	0	$ 0	0
Issuance/(cancellation) of non-vested stock (shares)		29,461
Exercise of stock options	1,763		1,763
Exercise of stock options (in shares)		49,988
Non-cash compensation	6,725		6,725
Surrendered Shares	(2,334)			(2,334)
Noncontrolling interest distribution	(12)						(12)
Net income	35,147					34,674	473
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