Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Capital Stock, Common	Additional Paid-in Capital	Retained Earnings	Treasury Stock
Balance at Dec. 31, 2017	$ 574,645	$ 907	$ 3,518	$ 694,174	$ (123,954)
Net income	72,677	0	0	72,677	0
Dividends on common stock	(6,589)	0	0	(6,589)	0
Stock-based compensation, net of tax	326	0	(64)	0	390
Stock Repurchased During Period, Value	(25,087)	0	0	0	(25,087)
Balance at Dec. 31, 2018	615,972	907	3,454	760,262	(148,651)
Net income	72,967	0	0	72,967	0
Dividends on common stock	(6,563)	0	0	(6,563)	0
Stock-based compensation, net of tax	1,533	0	574	0	959
Stock Issued During Period, Value	750	0	113	0	637
Balance at Dec. 31, 2019	684,659	907	4,141	826,666	(147,055)
Net income	70,806	0	0	70,806	0
Dividends on common stock	(6,502)	0	0	(6,502)	0
Stock-based compensation, net of tax	1,510	0	189	0	1,321
Stock Repurchased During Period, Value	(26,139)	0	0	0	(26,139)
Balance at Dec. 31, 2020	$ 724,334	$ 907	$ 4,330	$ 890,970	$ (171,873)