Consolidated Statements Of Shareholders' Equity (USD $) In Thousands, except Share data, unless otherwise specified	Total	Common Stock	Additional Paid-In Capital	Retained Earnings	Accumulated other Comprehensive Income (Loss)
Beginning Balance at Dec. 31, 2011	$ 500,056	$ 684	$ 165,518	$ 321,831	$ 12,023
Beginning Balance (in shares) at Dec. 31, 2011		68,430,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Employee stock compensation	35,420	2	35,418
Employee stock compensation (in shares)		174,000
Proceeds from stock issuances under employee plans	41,696	17	41,679
Proceeds from stock issuances under employee plans (in shares)		1,692,000
Tax effect of exercise of stock options	29,892		29,892
Cash dividends declared ($1.92 per share, $1.68 per share and $1.48 per share in 2014, 2013, and 2012 respectively)	(101,534)			(101,534)
Repurchase and retirement of common shares	(127,525)	(17)	(3,992)	(123,516)
Repurchase and retirement of common shares (in shares)	(1,649,000)	(1,649,000)
Net income	312,310			312,310
Other comprehensive income	215				215
Ending Balance at Dec. 31, 2012	690,530	686	268,515	409,091	12,238
Ending Balance (in shares) at Dec. 31, 2012		68,647,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Employee stock compensation	57,893	3	57,890
Deferred compensation	(8,421)		(4,358)	(4,063)
Employee stock compensation (in shares)		264,000
Proceeds from stock issuances under employee plans	26,922	10	26,912
Proceeds from stock issuances under employee plans (in shares)		1,049,000
Tax effect of exercise of stock options	28,621		28,621
Cash dividends declared ($1.92 per share, $1.68 per share and $1.48 per share in 2014, 2013, and 2012 respectively)	(113,722)			(113,722)
Repurchase and retirement of common shares	(530,033)	(43)	(16,964)	(513,026)
Repurchase and retirement of common shares (in shares)	(4,337,000)	(4,337,000)
Net income	377,292			377,292
Other comprehensive income	6,523				6,523
Ending Balance at Dec. 31, 2013	535,605	656	360,616	155,572	18,761
Ending Balance (in shares) at Dec. 31, 2013		65,623,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Employee stock compensation	63,183	3	63,180
Deferred compensation	(5,107)		(3,020)	(2,087)
Employee stock compensation (in shares)		254,000
Proceeds from stock issuances under employee plans	31,313	10	31,303
Proceeds from stock issuances under employee plans (in shares)		984,000
Tax effect of exercise of stock options	36,966		36,966
Cash dividends declared ($1.92 per share, $1.68 per share and $1.48 per share in 2014, 2013, and 2012 respectively)	(126,908)			(126,908)
Repurchase and retirement of common shares	(81,812)	(6)	(3,040)	(78,766)
Repurchase and retirement of common shares (in shares)	(554,000)	(554,000)
Net income	454,029			454,029
Other comprehensive income	(46,002)				(46,002)
Ending Balance at Dec. 31, 2014	$ 861,267	$ 663	$ 486,005	$ 401,840	$ (27,241)
Ending Balance (in shares) at Dec. 31, 2014		66,307,000