Consolidated Statement of Changes in Shareholders' Equity (USD $) In Thousands	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss), Net of Tax [Member]	Treasury Stock [Member]
Beginning balance at Dec. 31, 2009	$ 1,894,424	$ 602	$ 600,355	$ 1,150,103	$ 154,205	$ (10,841)
Net income	208,764			208,764
Other comprehensive income (loss), net of tax	45				45
Stock option exercises/deferred stock unit conversions	38,807	7	31,191	(1,225)		8,834
Tax benefits from stock-based compensation	419		419
Stock-based compensation expense recognized in earnings	14,925		14,925
Non-vested stock awards			(793)			793
Purchase of treasury stock	(986)					(986)
Treasury stock issued/sold to the 401(k) stock purchase plan	2,069			(131)		2,200
Common stock issued/sold to the 401(k) stock purchase plan	11,240	2	11,238
Cash dividends	(108,027)			(108,027)
Ending balance at Dec. 31, 2010	2,061,680	611	657,335	1,249,484	154,250
Net income	217,535			217,535
Other comprehensive income (loss), net of tax	93,484				93,484
Stock option exercises/deferred stock unit conversions	7,438	1	7,065	(50)		422
Tax benefits from stock-based compensation	316		316
Stock-based compensation expense recognized in earnings	15,963		15,963
Non-vested stock awards			(1,235)			1,235
Purchase of treasury stock	(2,029)					(2,029)
Common stock issued/sold to the 401(k) stock purchase plan	1,360	1	1,359
Cash dividends	(112,210)			(112,210)
Ending balance at Dec. 31, 2011	2,283,537	613	680,803	1,354,759	247,734	(372)
Net income	237,952			237,952
Other comprehensive income (loss), net of tax	(9,686)				(9,686)
Stock option exercises/deferred stock unit conversions	10,516	2	10,100	(6)		420
Tax benefits from stock-based compensation	(384)		(384)
Stock-based compensation expense recognized in earnings	12,836		12,836
Non-vested stock awards			(387)	(1)		388
Purchase of treasury stock	(436)					(436)
Cash dividends	(116,853)			(116,853)
Ending balance at Dec. 31, 2012	$ 2,417,482	$ 615	$ 702,968	$ 1,475,851	$ 238,048