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, 2017	$ 516,426	$ 35	$ 568,780	$ (53,713)	$ 15	$ 204	$ 1,105
Balance (in shares) at Dec. 31, 2017		35,747,134
Issuance of stock - employee stock purchase plan	1,157		1,157
Issuance of stock - employee stock purchase plan (shares)		24,236
Issuance of stock - 401(k) plan	4,781		4,781
Issuance of stock - 401(k) plan (shares)		84,959
Issuance/(cancellation) of non-vested stock	0	$ 1	(1)
Issuance/(cancellation) of non-vested stock (shares)		106,713
Exercise of stock options	2,609		2,609
Exercise of stock options (in shares)		81,135
Non-cash compensation	7,811		7,811
Surrendered Shares	(2,832)			(2,832)
Shares repurchased	(181,402)			(181,402)
Noncontrolling interest distribution	(350)						(350)
Net income	60,861					60,508	353
Balance, Stockholders Equity at Jun. 30, 2018	409,061	$ 36	585,137	(237,947)	15	60,712	1,108
Balance (in shares) at Jun. 30, 2018		36,044,177
Balance, Stockholders Equity at Mar. 31, 2018	549,558	$ 35	575,925	(55,018)	15	27,363	1,238
Balance (in shares) at Mar. 31, 2018		35,861,469
Issuance of stock - employee stock purchase plan	560		560
Issuance of stock - employee stock purchase plan (shares)		10,913
Issuance of stock - 401(k) plan	2,402		2,402
Issuance of stock - 401(k) plan (shares)		39,810
Issuance/(cancellation) of non-vested stock	0	$ 1	(1)
Issuance/(cancellation) of non-vested stock (shares)		53,462
Exercise of stock options	2,484		2,484
Exercise of stock options (in shares)		78,523
Non-cash compensation	3,767		3,767
Surrendered Shares	(1,527)			(1,527)
Shares repurchased	(181,402)			(181,402)
Noncontrolling interest distribution	(322)						(322)
Net income	33,541					33,349	192
Balance, Stockholders Equity at Jun. 30, 2018	409,061	$ 36	585,137	(237,947)	15	60,712	1,108
Balance (in shares) at Jun. 30, 2018		36,044,177
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
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
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