Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Capital Stock, Common	Additional Paid-in Capital	Retained Earnings [Member]	Treasury Stock
Balance at Dec. 31, 2017	$ 574,645	$ 907	$ 3,518	$ 694,174	$ (123,954)
Net income	13,378	0	0	13,378	0
Dividends on common stock, $0.02 per share	(1,667)	0	0	(1,667)	0
Repurchases of common stock	(1,293)	0	0	0	(1,293)
Stock-based compensation, net of tax	26	0	(104)	0	130
Balance at Mar. 31, 2018	585,089	907	3,414	705,885	(125,117)
Balance at Dec. 31, 2017	574,645	907	3,518	694,174	(123,954)
Net income	31,182
Balance at Jun. 30, 2018	581,789	907	3,462	722,045	(144,625)
Balance at Mar. 31, 2018	585,089	907	3,414	705,885	(125,117)
Net income	17,803	0	0	17,803	0
Dividends on common stock, $0.02 per share	(1,643)	0	0	(1,643)	0
Repurchases of common stock	(19,629)	0	0	0	(19,629)
Stock-based compensation, net of tax	169	0	48	0	121
Balance at Jun. 30, 2018	581,789	907	3,462	722,045	(144,625)
Balance at Dec. 31, 2018	615,972	907	3,454	760,262	(148,651)
Net income	17,318	0	0	17,318	0
Dividends on common stock, $0.02 per share	(1,640)	0	0	(1,640)	0
Stock-based compensation, net of tax	177	0	(30)	0	207
Balance at Mar. 31, 2019	631,827	907	3,424	775,940	(148,444)
Balance at Dec. 31, 2018	615,972	907	3,454	760,262	(148,651)
Net income	39,679			39,679
Balance at Jun. 30, 2019	653,329	907	3,799	796,661	(148,038)
Balance at Mar. 31, 2019	631,827	907	3,424	775,940	(148,444)
Net income	22,361	0	0	22,361	0
Dividends on common stock, $0.02 per share	(1,640)	0	0	(1,640)	0
Stock-based compensation, net of tax	781	0	375	0	406
Balance at Jun. 30, 2019	$ 653,329	$ 907	$ 3,799	$ 796,661	$ (148,038)