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, 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
Balance at Dec. 31, 2019	35,811	860,671	1,425,752	(1,597,940)	2,314	726,608
Net income			205,714			205,714
Dividends paid			(15,639)			(15,639)
Stock awards and exercise of stock options	326	64,948		(32,716)		32,558
Purchases of treasury stock				(147,123)		(147,123)
Other		(348)	(362)	(30)	30	(710)
Balance at Sep. 30, 2020	36,137	925,271	1,615,465	(1,777,809)	2,344	801,408
Balance at Jun. 30, 2020	36,040	904,421	1,553,144	(1,745,299)	2,390	750,696
Net income			67,722			67,722
Dividends paid			(5,401)			(5,401)
Stock awards and exercise of stock options	97	20,636		(7,581)		13,152
Purchases of treasury stock				(24,975)		(24,975)
Other		214		46	(46)	214
Balance at Sep. 30, 2020	$ 36,137	$ 925,271	$ 1,615,465	$ (1,777,809)	$ 2,344	$ 801,408