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			151,216			151,216
Dividends paid			(13,850)			(13,850)
Stock awards and exercise of stock options	479	59,749		(47,164)		13,064
Purchases of treasury stock				(121,976)		(121,976)
Other		(283)	(372)	(105)	105	(655)
Balance at Sep. 30, 2018	35,211	755,263	1,175,949	(1,400,577)	2,307	568,153
Balance at Jun. 30, 2018	35,141	744,228	1,129,289	(1,354,538)	2,271	556,391
Net income			51,249			51,249
Dividends paid			(4,834)			(4,834)
Stock awards and exercise of stock options	70	10,679		(8,331)		2,418
Purchases of treasury stock				(37,672)		(37,672)
Other		356	245	(36)	36	601
Balance at Sep. 30, 2018	35,211	755,263	1,175,949	(1,400,577)	2,307	568,153
Balance at Dec. 31, 2018	35,311	774,358	1,225,617	(1,446,296)	2,344	591,334
Net income			154,343			154,343
Dividends paid			(14,657)			(14,657)
Stock awards and exercise of stock options	427	67,149		(54,620)		12,956
Purchases of treasury stock				(71,926)		(71,926)
Other		330		(2)	2	330
Balance at Sep. 30, 2019	35,738	841,837	1,365,303	(1,572,844)	2,346	672,380
Balance at Jun. 30, 2019	35,591	817,255	1,311,446	(1,548,138)	2,415	618,569
Net income			58,947			58,947
Dividends paid			(5,090)			(5,090)
Stock awards and exercise of stock options	147	24,660		(24,775)		32
Other		(78)		69	(69)	(78)
Balance at Sep. 30, 2019	$ 35,738	$ 841,837	$ 1,365,303	$ (1,572,844)	$ 2,346	$ 672,380