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			95,396			95,396
Dividends paid			(9,567)			(9,567)
Stock awards and exercise of stock options	280	42,489		(29,845)		12,924
Purchases of treasury stock				(71,926)		(71,926)
Other		408		(71)	71	408
Balance at Jun. 30, 2019	35,591	817,255	1,311,446	(1,548,138)	2,415	618,569
Balance at Mar. 31, 2019	35,521	803,701	1,265,485	(1,519,077)	2,380	588,010
Net income			50,729			50,729
Dividends paid			(4,768)			(4,768)
Stock awards and exercise of stock options	70	13,337		(6,350)		7,057
Purchases of treasury stock				(22,676)		(22,676)
Other		217		(35)	35	217
Balance at Jun. 30, 2019	35,591	817,255	1,311,446	(1,548,138)	2,415	618,569
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