CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Cumulative Effect, Period of Adoption, Adjustment [Member] Retained Earnings	Cumulative Effect, Period of Adoption, Adjustment [Member]	Common Stock	Treasury Stock	Additional Paid-In Capital	Retained Earnings	Total
BALANCE at Dec. 31, 2017			$ 411	$ (63,519)	$ 312,784	$ 168,269	$ 417,945
BALANCE (in shares) at Dec. 31, 2017			41,123,365
BALANCE (in shares) at Dec. 31, 2017				(3,936,291)
Increase (Decrease) in Stockholders' Equity
Net income						112,903	112,903
Issuance of Stock:
Issuance of shares for options exercised				$ 3,618	(513)		3,105
Issuance of shares for options exercised (in shares)				206,875
Issuance of restricted stock & performance stock				$ 2,227	(4)		2,223
Issuance of restricted stock & performance stock (in shares)				129,569
Shares received in lieu of tax withholding payment on vested restricted stock				$ (1,540)			(1,540)
Shares received in lieu of tax withholding payment on vested restricted stock (in shares)				(36,967)
Stock-based compensation					4,212		4,212
Dividends						(12,268)	(12,268)
Share repurchase				$ (28,533)			(28,533)
Share repurchase (in shares)				(592,839)
BALANCE at Dec. 31, 2018			$ 411	$ (87,747)	316,479	268,904	498,047
BALANCE (in shares) at Dec. 31, 2018			41,123,365
BALANCE (in shares) at Dec. 31, 2018				(4,229,653)
Increase (Decrease) in Stockholders' Equity
Net income						114,324	114,324
Issuance of Stock:
Issuance of shares for options exercised				$ 2,532	(182)		2,350
Issuance of shares for options exercised (in shares)				114,125
Issuance of restricted stock & performance stock				$ 2,303	(297)		2,006
Issuance of restricted stock & performance stock (in shares)				107,606
Shares received in lieu of tax withholding payment on vested restricted stock				$ (1,498)			(1,498)
Shares received in lieu of tax withholding payment on vested restricted stock (in shares)				(28,586)
Stock-based compensation					4,168		4,168
Dividends						(14,543)	(14,543)
Share repurchase				$ (19,550)			(19,550)
Share repurchase (in shares)				(428,940)
BALANCE at Dec. 31, 2019			$ 411	$ (103,960)	320,168	368,685	$ 585,304
BALANCE (in shares) at Dec. 31, 2019			41,123,365				41,123,365
BALANCE (in shares) at Dec. 31, 2019				(4,465,448)			4,465,448
Increase (Decrease) in Stockholders' Equity
Net income						150,139	$ 150,139
Issuance of Stock:
Issuance of shares for options exercised				$ 2,811	(667)		2,144
Issuance of shares for options exercised (in shares)				113,731
Issuance of restricted stock & performance stock				$ 3,102	(1,247)		1,855
Issuance of restricted stock & performance stock (in shares)				128,889
Shares received in lieu of tax withholding payment on vested restricted stock				$ (1,076)			(1,076)
Shares received in lieu of tax withholding payment on vested restricted stock (in shares)				(27,724)
Stock-based compensation					4,197		4,197
Dividends						(15,499)	(15,499)
Share repurchase				$ (30,120)			(30,120)
Share repurchase (in shares)				(684,634)
BALANCE at Dec. 31, 2020	$ (515)	$ (515)	$ 411	$ (129,243)	$ 322,451	$ 502,810	$ 696,429
BALANCE (in shares) at Dec. 31, 2020			41,123,365				41,123,365
BALANCE (in shares) at Dec. 31, 2020				(4,935,186)			4,935,186