Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Deferred Compensation Trust [Member]	Retained Earnings [Member]
Beginning Balance at Dec. 31, 2013	$ 304,792	$ 24	$ 213,648	$ (2,246)	$ 93,366
Beginning Balance, Shares at Dec. 31, 2013		24,478,544
Stock compensation, including options and long-term incentives	3,393		3,393
Stock compensation, including options and long-term incentives, Shares		6,023
Director deferred shares for annual deferral elections	773		773
Exercise of stock options, including tax benefits	6,652	$ 1	6,651
Exercise of stock options, including tax benefits, Shares		318,321
Shares issued for long-term incentive awards, net of shares withheld for taxes	(1,667)		(1,667)
Shares issued for long-term incentive awards, net of shares withheld for taxes, Shares		68,918
Deferred tax adjustment for long-term incentive plan	971		971
Purchase of shares by Deferred Compensation Trust	(53)			(53)
Sale of shares by Deferred Compensation Trust	54		(56)	110
Net income	51,991				51,991
Ending Balance at Dec. 31, 2014	366,906	$ 25	223,713	(2,189)	145,357
Ending Balance, Shares at Dec. 31, 2014		24,871,806
Stock compensation, including options and long-term incentives	2,983		2,983
Stock compensation, including options and long-term incentives, Shares		37,311
Director deferred shares for annual deferral elections	895		895
Exercise of stock options, including tax benefits	2,533		2,533
Exercise of stock options, including tax benefits, Shares		116,088
Shares issued for long-term incentive awards, net of shares withheld for taxes	(3,118)		(3,118)
Shares issued for long-term incentive awards, net of shares withheld for taxes, Shares		116,594
Deferred tax adjustment for long-term incentive plan	2,674		2,674
Purchase of shares by Deferred Compensation Trust	(2,227)			(2,227)
Sale of shares by Deferred Compensation Trust	2,227		913	1,314
Net income	55,016				55,016
Ending Balance at Dec. 31, 2015	427,889	$ 25	230,593	(3,102)	200,373
Ending Balance, Shares at Dec. 31, 2015		25,141,799
Stock compensation, including options and long-term incentives	3,562		3,562
Stock compensation, including options and long-term incentives, Shares		12,358
Director deferred shares for annual deferral elections	1,037		1,037
Exercise of stock options, including tax benefits	$ 3,173		3,173
Exercise of stock options, including tax benefits, Shares	124,065	124,065
Shares issued for long-term incentive awards, net of shares withheld for taxes	$ (651)		(651)
Shares issued for long-term incentive awards, net of shares withheld for taxes, Shares		44,479
Deferred tax adjustment for long-term incentive plan	44		44
Purchase of shares by Deferred Compensation Trust	(203)		88	(291)
Sale of shares by Deferred Compensation Trust	203			203
Net income	48,024				48,024
Ending Balance at Dec. 31, 2016	$ 483,078	$ 25	$ 237,846	$ (3,190)	$ 248,397
Ending Balance, Shares at Dec. 31, 2016		25,322,701