CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	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				16,659	16,659
Issuance of Stock:
Issuance of shares for options exercised		$ 326	(88)		238
Issuance of shares for options exercised (in shares)		19,124
Issuance of restricted stock & performance stock		$ 892	1,331		2,223
Issuance of restricted stock & performance stock (in shares)		52,306
Shares received in lieu of tax withholding payment on vested restricted stock		$ (846)			(846)
Shares received in lieu of tax withholding payment on vested restricted stock (in shares)		(19,921)
Stock-based compensation			1,880		1,880
Dividends				(2,786)	(2,786)
Share repurchase		$ (6,175)			(6,175)
Share repurchase (in shares)		(150,481)
BALANCE at Mar. 31, 2018	$ 411	$ (69,323)	315,907	182,142	429,138
BALANCE (in shares) at Mar. 31, 2018	41,123,365
BALANCE (in shares) at Mar. 31, 2018		(4,035,263)
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					49,206
BALANCE at Jun. 30, 2018	$ 411	$ (67,386)	316,235	211,715	460,975
BALANCE (in shares) at Jun. 30, 2018	41,123,365
BALANCE (in shares) at Jun. 30, 2018		(3,877,756)
BALANCE at Mar. 31, 2018	$ 411	$ (69,323)	315,907	182,142	429,138
BALANCE (in shares) at Mar. 31, 2018	41,123,365
BALANCE (in shares) at Mar. 31, 2018		(4,035,263)
Increase (Decrease) in Stockholders' Equity
Net income				32,547	32,547
Issuance of Stock:
Issuance of shares for options exercised		$ 1,949	(29)		1,920
Issuance of shares for options exercised (in shares)		112,616
Issuance of restricted stock & performance stock		$ 1,335	(1,335)		0
Issuance of restricted stock & performance stock (in shares)		77,263
Shares received in lieu of tax withholding payment on vested restricted stock		$ (693)			(693)
Shares received in lieu of tax withholding payment on vested restricted stock (in shares)		(17,046)
Stock-based compensation			1,692		1,692
Dividends				(2,974)	(2,974)
Share repurchase		$ (654)			(654)
Share repurchase (in shares)		(15,326)
BALANCE at Jun. 30, 2018	$ 411	$ (67,386)	316,235	211,715	460,975
BALANCE (in shares) at Jun. 30, 2018	41,123,365
BALANCE (in shares) at Jun. 30, 2018		(3,877,756)
BALANCE at Dec. 31, 2018	$ 411	$ (87,747)	316,479	268,904	$ 498,047
BALANCE (in shares) at Dec. 31, 2018	41,123,365				41,123,365
BALANCE (in shares) at Dec. 31, 2018		(4,229,653)			4,229,653
Increase (Decrease) in Stockholders' Equity
Net income				19,866	$ 19,866
Issuance of Stock:
Issuance of shares for options exercised		$ 861	(61)		800
Issuance of shares for options exercised (in shares)		41,103
Issuance of restricted stock & performance stock		$ 817	1,189		2,006
Issuance of restricted stock & performance stock (in shares)		38,539
Shares received in lieu of tax withholding payment on vested restricted stock		$ (781)			(781)
Shares received in lieu of tax withholding payment on vested restricted stock (in shares)		(15,013)
Stock-based compensation			2,084		2,084
Dividends				(3,506)	(3,506)
Share repurchase		$ (3,321)			(3,321)
Share repurchase (in shares)		(67,394)
BALANCE at Mar. 31, 2019	$ 411	$ (90,171)	319,691	285,264	515,195
BALANCE (in shares) at Mar. 31, 2019	41,123,365
BALANCE (in shares) at Mar. 31, 2019		(4,232,418)
BALANCE at Dec. 31, 2018	$ 411	$ (87,747)	316,479	268,904	$ 498,047
BALANCE (in shares) at Dec. 31, 2018	41,123,365				41,123,365
BALANCE (in shares) at Dec. 31, 2018		(4,229,653)			4,229,653
Increase (Decrease) in Stockholders' Equity
Net income					$ 44,039
BALANCE at Jun. 30, 2019	$ 411	$ (93,947)	319,879	305,745	$ 532,088
BALANCE (in shares) at Jun. 30, 2019	41,123,365				41,123,365
BALANCE (in shares) at Jun. 30, 2019		(4,268,984)			4,268,984
BALANCE at Mar. 31, 2019	$ 411	$ (90,171)	319,691	285,264	$ 515,195
BALANCE (in shares) at Mar. 31, 2019	41,123,365
BALANCE (in shares) at Mar. 31, 2019		(4,232,418)
Increase (Decrease) in Stockholders' Equity
Net income				24,173	24,173
Issuance of Stock:
Issuance of shares for options exercised		$ 31	(11)		20
Issuance of shares for options exercised (in shares)		1,408
Issuance of restricted stock & performance stock		$ 1,486	(1,486)
Issuance of restricted stock & performance stock (in shares)		69,067
Shares received in lieu of tax withholding payment on vested restricted stock		$ (717)			(717)
Shares received in lieu of tax withholding payment on vested restricted stock (in shares)		(13,573)
Stock-based compensation			1,685		1,685
Dividends				(3,692)	(3,692)
Share repurchase		$ (4,576)			(4,576)
Share repurchase (in shares)		(93,468)
BALANCE at Jun. 30, 2019	$ 411	$ (93,947)	$ 319,879	$ 305,745	$ 532,088
BALANCE (in shares) at Jun. 30, 2019	41,123,365				41,123,365
BALANCE (in shares) at Jun. 30, 2019		(4,268,984)			4,268,984