Condensed 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, 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
Beginning Balance at Dec. 31, 2019	815,226	$ 26	260,871	(3,871)	558,200
Beginning Balance, Shares at Dec. 31, 2019		25,936,532
Stock compensation, including options and long-term incentives	1,317		1,317
Exercise of stock options less shares withheld for taxes	2,137		2,137
Exercise of stock options less shares withheld for taxes, Shares		69,640
Shares issued for long-term incentive awards, net of shares withheld for taxes, Shares		57,176
Shares issued for long-term incentive awards, net of shares withheld for taxes	(3,404)		(3,404)
Purchase of shares by Deferred Compensation Trust			1,146	(1,146)
Sale of shares by Deferred Compensation Trust			(59)	59
Net income	28,111				28,111
Ending Balance at Mar. 31, 2020	$ 843,387	$ 26	$ 262,008	$ (4,958)	$ 586,311
Ending Balance, Shares at Mar. 31, 2020		26,063,348