Consolidated Statements Of Changes In Stockholders' Equity - USD ($) $ in Thousands	Capital Stock [Member]	Paid-In Capital [Member]	Retained Earnings [Member]	Treasury Stock-At Cost [Member]	Deferred Compensation Payable In Company Stock [Member]	Total
Balance at Dec. 31, 2017	$ 34,732	$ 695,797	$ 1,038,955	$ (1,231,332)	$ 2,202	$ 540,354
Net income			44,996			44,996
Dividends paid			(4,533)			(4,533)
Stock awards and exercise of stock options	153	17,410		(9,352)		8,211
Purchases of treasury stock				(81,125)		(81,125)
Other		(216)	(728)	(34)	34	(944)
Balance at Mar. 31, 2018	34,885	712,991	1,078,690	(1,321,843)	2,236	506,959
Balance at Dec. 31, 2018	35,311	774,358	1,225,617	(1,446,296)	2,344	591,334
Net income			44,667			44,667
Dividends paid			(4,799)			(4,799)
Stock awards and exercise of stock options	210	29,152		(23,495)		5,867
Purchases of treasury stock				(49,250)		(49,250)
Other		191		(36)	36	191
Balance at Mar. 31, 2019	$ 35,521	$ 803,701	$ 1,265,485	$ (1,519,077)	$ 2,380	$ 588,010