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			205,544			205,544
Dividends paid			(18,662)			(18,662)
Stock awards and exercise of stock options (Note 4)	579	79,452		(55,939)		24,092
Purchases of treasury stock (Note 18)				(158,884)		(158,884)
Other		(891)	(220)	(141)	142	(1,110)
Balance at Dec. 31, 2018	35,311	774,358	1,225,617	(1,446,296)	2,344	591,334
Net income			219,923			219,923
Dividends paid			(19,788)			(19,788)
Stock awards and exercise of stock options (Note 4)	500	85,788		(59,043)		27,245
Purchases of treasury stock (Note 18)				(92,631)		(92,631)
Other		525		30	(30)	525
Balance at Dec. 31, 2019	35,811	860,671	1,425,752	(1,597,940)	2,314	726,608
Net income			319,466			319,466
Dividends paid			(21,079)			(21,079)
Stock awards and exercise of stock options (Note 4)	448	100,427		(49,020)		51,855
Purchases of treasury stock (Note 18)				(175,594)		(175,594)
Other		306	(362)	(25)	25	(56)
Balance at Dec. 31, 2020	$ 36,259	$ 961,404	$ 1,723,777	$ (1,822,579)	$ 2,339	$ 901,200