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	2,384		2,384
Issuance of stock - employee stock purchase plan (shares)		23,267
Issuance of stock - 401(k) plan	6,966		6,966
Issuance of stock - 401(k) plan (shares)		57,783
Issuance/(cancellation) of non-vested stock	0	$ 1	(1)
Issuance/(cancellation) of non-vested stock (shares)		185,515
Exercise of stock options	3,388		3,388
Exercise of stock options (in shares)		80,428
Non-cash compensation	18,451		18,451
Surrendered Shares	(9,385)			(9,385)
Noncontrolling interest distribution	(910)						(910)
Net income	99,938					99,178	760
Balance, Stockholders Equity at Sep. 30, 2019	603,465	$ 37	634,854	(251,070)	15	218,728	901
Balance (in shares) at Sep. 30, 2019		36,599,273
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
Issuance of stock - employee stock purchase plan	850		850
Issuance of stock - employee stock purchase plan (shares)		8,230
Issuance of stock - 401(k) plan	2,353		2,353
Issuance of stock - 401(k) plan (shares)		19,381
Issuance/(cancellation) of non-vested stock	0	$ 1	(1)
Issuance/(cancellation) of non-vested stock (shares)		88,334
Exercise of stock options	2,045		2,045
Exercise of stock options (in shares)		37,737
Non-cash compensation	6,298		6,298
Surrendered Shares	(4,895)			(4,895)
Noncontrolling interest distribution	(453)						(453)
Net income	34,325					34,132	193
Balance, Stockholders Equity at Sep. 30, 2019	603,465	$ 37	634,854	(251,070)	15	218,728	901
Balance (in shares) at Sep. 30, 2019		36,599,273
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		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