Consolidated Statement Of Changes In Shareholders' Equity (USD $) In Thousands, unless otherwise specified	Common Stock [Member]	Additional Paid-In Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss), Net Of Tax [Member]	Treasury Stock [Member]	Total
Balance at Dec. 31, 2008	$ 602	$ 589,065	$ 1,080,160	$ 137,294	$ (43,594)	$ 1,763,527
Comprehensive income:
Net income			179,034			179,034
Other comprehensive income, net of tax				16,911		16,911
Total comprehensive income						195,945
Stock option exercises/deferred stock unit conversions (shares)			(6,147)		22,373	16,226
Tax benefits from stock-based compensation		1,496				1,496
Stock-based compensation expense recognized in earnings		12,645				12,645
Non-vested stock awards		(2,851)	(176)		3,027
Purchase of treasury stock					(800)	(800)
Treasury stock issued/sold to the 401(k) stock purchase plan			(638)		8,153	7,515
Cash dividends			(102,130)			(102,130)
Balance at Dec. 31, 2009	602	600,355	1,150,103	154,205	(10,841)	1,894,424
Comprehensive income:
Net income			208,764			208,764
Other comprehensive income, net of tax				45		45
Total comprehensive income						208,809
Stock option exercises/deferred stock unit conversions (shares)	7	31,191	(1,225)		8,834	38,807
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			(131)		2,200	2,069
Common stock issued/sold to the 401(k) stock purchase plan	2	11,238				11,240
Cash dividends			(108,027)			(108,027)
Balance at Dec. 31, 2010	611	657,335	1,249,484	154,250		2,061,680
Comprehensive income:
Net income			217,535			217,535
Other comprehensive income, net of tax				93,484		93,484
Total comprehensive income						311,019
Stock option exercises/deferred stock unit conversions (shares)	1	7,065	(50)		422	7,438
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	1,359				1,360
Cash dividends			(112,210)			(112,210)
Balance at Dec. 31, 2011	$ 613	$ 680,803	$ 1,354,759	$ 247,734	$ (372)	$ 2,283,537