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			99,967			99,967
Dividends paid			(9,016)			(9,016)
Stock awards and exercise of stock options	409	49,070		(38,833)		10,646
Purchases of treasury stock				(84,304)		(84,304)
Other		(639)	(617)	(69)	69	(1,256)
Balance at Jun. 30, 2018	35,141	744,228	1,129,289	(1,354,538)	2,271	556,391
Balance at Mar. 31, 2018	34,885	712,991	1,078,690	(1,321,843)	2,236	506,959
Net income			54,971			54,971
Dividends paid			(4,483)			(4,483)
Stock awards and exercise of stock options	256	31,660		(29,481)		2,435
Purchases of treasury stock				(3,179)		(3,179)
Other		(423)	111	(35)	35	(312)
Balance at Jun. 30, 2018	35,141	744,228	1,129,289	(1,354,538)	2,271	556,391
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