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, 2019	$ 35,811	$ 860,671	$ 1,425,752	$ (1,597,940)	$ 2,314	$ 726,608
Net income			137,992			137,992
Dividends paid			(10,238)			(10,238)
Stock awards and exercise of stock options	229	44,312		(25,135)		19,406
Purchases of treasury stock				(122,148)		(122,148)
Other		(562)	(362)	(76)	76	(924)
Balance at Jun. 30, 2020	36,040	904,421	1,553,144	(1,745,299)	2,390	750,696
Balance at Mar. 31, 2020	35,912	878,550	1,476,151	(1,709,390)	2,378	683,601
Net income			82,101			82,101
Dividends paid			(5,108)			(5,108)
Stock awards and exercise of stock options	128	25,340		(13,995)		11,473
Purchases of treasury stock				(21,914)		(21,914)
Other		531			12	543
Balance at Jun. 30, 2020	36,040	904,421	1,553,144	(1,745,299)	2,390	750,696
Balance at Dec. 31, 2020	36,259	961,404	1,723,777	(1,822,579)	2,339	901,200
Net income			121,922			121,922
Dividends paid			(10,864)			(10,864)
Stock awards and exercise of stock options	126	37,637		(13,255)		24,508
Purchases of treasury stock				(166,649)		(166,649)
Other		656		157	(156)	657
Balance at Jun. 30, 2021	36,385	999,697	1,834,835	(2,002,326)	2,183	870,774
Balance at Mar. 31, 2021	36,345	982,739	1,783,740	(1,876,315)	2,375	928,884
Net income			56,522			56,522
Dividends paid			(5,427)			(5,427)
Stock awards and exercise of stock options	40	16,630		(4,323)		12,347
Purchases of treasury stock				(121,882)		(121,882)
Other		328		194	(192)	330
Balance at Jun. 30, 2021	$ 36,385	$ 999,697	$ 1,834,835	$ (2,002,326)	$ 2,183	$ 870,774