Consolidated Statements Of Shareholders' Equity (USD $) In Thousands, except Share data	Total	Common Stock	Additional Paid-In Capital	Retained Earnings	Accumulated other Comprehensive Income (Loss)
Beginning Balance at Dec. 31, 2009	$ 204,541	$ 653	$ 9,990	$ 191,074	$ 2,824
Beginning Balance (in shares) at Dec. 31, 2009		65,296,000
Employee stock compensation (in shares)		308,000
Employee stock compensation	18,052	3	18,049
Proceeds from stock issuances under employee plans (in shares)		4,066,000
Proceeds from stock issuances under employee plans	68,105	41	68,064
Tax effect of exercise of stock options	10,610		10,610
Cash dividends declared ($1.48 per share, $0.90 per share and $0.80 per share in 2012, 2011, and 2010 respectively)	(53,043)			(53,043)
Repurchase and retirement of common shares (in shares)	(1,202,000)	(1,202,000)
Repurchase and retirement of common shares	(27,486)	(12)	(27,474)
Net Income	147,138			147,138
Other comprehensive income	3,074				3,074
Ending Balance at Dec. 31, 2010	370,991	685	79,239	285,169	5,898
Ending Balance (in shares) at Dec. 31, 2010		68,468,000
Employee stock compensation (in shares)		290,000
Employee stock compensation	20,548	3	20,545
Proceeds from stock issuances under employee plans (in shares)		2,280,000
Proceeds from stock issuances under employee plans	45,654	22	45,632
Tax effect of exercise of stock options	23,120		23,120
Cash dividends declared ($1.48 per share, $0.90 per share and $0.80 per share in 2012, 2011, and 2010 respectively)	(61,585)			(61,585)
Repurchase and retirement of common shares (in shares)	(2,608,000)	(2,608,000)
Repurchase and retirement of common shares	(132,372)	(26)	(3,018)	(129,328)
Net Income	227,575			227,575
Other comprehensive income	6,125				6,125
Ending Balance at Dec. 31, 2011	500,056	684	165,518	321,831	12,023
Ending Balance (in shares) at Dec. 31, 2011		68,430,000
Employee stock compensation (in shares)		174,000
Employee stock compensation	35,420	2	35,418
Proceeds from stock issuances under employee plans (in shares)		1,692,000
Proceeds from stock issuances under employee plans	41,696	17	41,679
Tax effect of exercise of stock options	29,892		29,892
Cash dividends declared ($1.48 per share, $0.90 per share and $0.80 per share in 2012, 2011, and 2010 respectively)	(101,534)			(101,534)
Repurchase and retirement of common shares (in shares)	(1,649,000)	(1,649,000)
Repurchase and retirement of common shares	(127,525)	(17)	(3,992)	(123,516)
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