Consolidated Statements Of Shareholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Retained Earnings	Accumulated other Comprehensive Income (Loss)
Beginning Balance at Dec. 31, 2014	$ 861,267	$ 663	$ 486,005	$ 401,840	$ (27,241)
Beginning Balance (in shares) at Dec. 31, 2014		66,307
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Employee stock compensation	61,929	$ 2	61,927
Deferred compensation	3,883		(2,994)	6,877
Employee stock compensation (in shares)		144
Proceeds from stock issuances under employee plans	32,535	$ 10	32,525
Proceeds from stock issuances under employee plans (in shares)		1,037
Tax effect of exercise of stock options	34,654		34,654
Cash dividends declared ($2.32 per share, $2.20 per share and $2.12 per share in 2017, 2016, and 2015 respectively)	(139,285)			(139,285)
Repurchase and retirement of common shares	$ (293,616)	$ (22)	(15,974)	(277,620)
Repurchase and retirement of common shares (in shares)	(2,179)	(2,179)
Net income	$ 455,361			455,361
Other comprehensive income	(35,251)				(35,251)
Ending Balance at Dec. 31, 2015	981,477	$ 653	596,143	447,173	(62,492)
Ending Balance (in shares) at Dec. 31, 2015		65,309
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Employee stock compensation	57,927	$ 3	57,924
Deferred compensation	917		1,379	(462)
Employee stock compensation (in shares)		303
Proceeds from stock issuances under employee plans	17,690	$ 4	17,686
Proceeds from stock issuances under employee plans (in shares)		405
Tax effect of exercise of stock options	3,578		3,578
Cash dividends declared ($2.32 per share, $2.20 per share and $2.12 per share in 2017, 2016, and 2015 respectively)	(140,336)			(140,336)
Repurchase and retirement of common shares	$ (245,816)	$ (29)	(26,548)	(219,239)
Repurchase and retirement of common shares (in shares)	(2,908)	(2,908)
Net income	$ 212,948			212,948
Other comprehensive income	(21,345)				(21,345)
Ending Balance at Dec. 31, 2016	867,040	$ 631	650,162	300,084	(83,837)
Ending Balance (in shares) at Dec. 31, 2016		63,109
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Employee stock compensation	50,054	$ 1	50,053
Deferred compensation	(2,989)		1,536	(4,525)
Employee stock compensation (in shares)		60
Proceeds from stock issuances under employee plans	42,738	$ 9	42,729
Proceeds from stock issuances under employee plans (in shares)		934
Cash dividends declared ($2.32 per share, $2.20 per share and $2.12 per share in 2017, 2016, and 2015 respectively)	(145,423)			(145,423)
Repurchase and retirement of common shares	$ (90,461)	$ (10)	(10,586)	(79,865)
Repurchase and retirement of common shares (in shares)	(1,028)	(1,028)
Net income	$ 172,492			172,492
Other comprehensive income	38,208				38,208
Ending Balance at Dec. 31, 2017	$ 931,659	$ 631	$ 733,894	$ 242,763	$ (45,629)
Ending Balance (in shares) at Dec. 31, 2017		63,075