Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Capital Stock, Common	Additional Paid-in Capital	Retained Earnings	Treasury Stock
Balance at Dec. 31, 2015	$ 469,928	$ 907	$ 4,126	$ 575,948	$ (111,053)
Net income	56,386	0	0	56,386	0
Dividends on common stock	(6,666)	0	0	(6,666)	0
Stock-based compensation, net of tax	856	0	(693)	0	1,549
Stock Repurchased During Period, Value	(14,678)	0	0	0	(14,678)
Balance at Dec. 31, 2016	505,826	907	3,433	625,668	(124,182)
Net income	75,173	0	0	75,173	0
Dividends on common stock	(6,667)	0	0	(6,667)	0
Stock-based compensation, net of tax	313	0	85	0	228
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)