Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Deferred Compensation Trust [Member]	Retained Earnings [Member]
Beginning Balance at Dec. 31, 2017	$ 582,494	$ 26	$ 246,454	$ (3,486)	$ 339,500
Beginning Balance, Shares at Dec. 31, 2017		25,551,617
Stock compensation, including options and long-term incentives	1,058		1,058
Exercise of stock options less shares withheld for taxes	4,018		4,018
Exercise of stock options less shares withheld for taxes, Shares		97,370
Shares issued for long-term incentive awards, net of shares withheld for taxes, Shares		31,428
Shares issued for long-term incentive awards, net of shares withheld for taxes	(1,302)		(1,302)
Purchase of shares by Deferred Compensation Trust	(290)		5	(295)
Sale of shares by Deferred Compensation Trust	291			291
Net income	21,125				21,125
Ending Balance at Mar. 31, 2018	607,394	$ 26	250,233	(3,490)	360,625
Ending Balance, Shares at Mar. 31, 2018		25,680,415
Beginning Balance at Dec. 31, 2018	695,864	$ 26	254,738	(3,381)	444,481
Beginning Balance, Shares at Dec. 31, 2018		25,693,651
Stock compensation, including options and long-term incentives	998		998
Director deferred share activity , Shares		45,075
Exercise of stock options less shares withheld for taxes	1,798		1,798
Exercise of stock options less shares withheld for taxes, Shares		68,169
Shares issued for long-term incentive awards, net of shares withheld for taxes, Shares		83,281
Shares issued for long-term incentive awards, net of shares withheld for taxes	(3,268)		(3,268)
Purchase of shares by Deferred Compensation Trust	(149)		309	(458)
Sale of shares by Deferred Compensation Trust	148			148
Net income	22,259				22,259
Ending Balance at Mar. 31, 2019	$ 717,650	$ 26	$ 254,575	$ (3,691)	$ 466,740
Ending Balance, Shares at Mar. 31, 2019		25,890,176