Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Capital Stock, Common	Additional Paid-in Capital	Retained Earnings	Treasury Stock
Balance at Dec. 31, 2014	$ 476,587	$ 907	$ 4,058	$ 509,834	$ (38,212)
Net income	73,056	0	0	73,056	0
Dividends on common stock	(6,942)	0	0	(6,942)	0
Stock-based compensation, net of tax	1,251	0	68	0	1,183
Stock Repurchased During Period, Value	(74,024)	0	0	0	(74,024)
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)