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, 2015	$ 981,477	$ 653	$ 596,143	$ 447,173	$ (62,492)
Beginning 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
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Employee stock compensation	63,966	$ 2	63,964
Deferred compensation	4,880		(111)	(4,769)
Employee stock compensation (in shares)		245
Proceeds from stock issuances under employee plans	47,092	$ 8	47,084
Proceeds from stock issuances under employee plans (in shares)		754
Cash dividends declared ($2.32 per share, $2.20 per share and $2.12 per share in 2017, 2016, and 2015 respectively)	(149,032)			149,032
Repurchase and retirement of common shares	$ (348,663)	$ 32	37,066	311,565
Repurchase and retirement of common shares (in shares)	(3,184)	3,184
Other activity	$ (800)		(1)	(799)
Net income	335,257			335,257
Other comprehensive income	(17,344)				(17,344)
Ending Balance at Dec. 31, 2018	$ 867,015	$ 609	$ 807,986	$ 121,393	$ (62,973)
Ending Balance (in shares) at Dec. 31, 2018		60,890