Consolidated Statements of Shareholders' Equity (USD $) In Thousands, unless otherwise specified	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income [Member]	Treasury Stock [Member]
Beginning Balance at Dec. 31, 2011	$ 1,992,539	$ 540,386	$ 1,423,727	$ 264,059	$ 7,955	$ (243,588)
Beginning Balance (in shares) at Dec. 31, 2011		200,164
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	78,023			78,023
Other Comprehensive Income (Loss)	(7,473)				(7,473)
Stock issued, including related tax benefits	3,157	1,201	(1,740)			3,696
Stock issued, including related tax benefits (in shares)		716
Stock-based compensation awards	3,050		3,050
Common stock cash dividends	(28,112)			(28,112)
Ending Balance at Jun. 30, 2012	2,041,184	541,587	1,425,037	313,970	482	(239,892)
Ending Balance (in shares) at Jun. 30, 2012		200,880
Beginning Balance at Dec. 31, 2012	2,081,656	542,093	1,426,267	363,937	5,675	(256,316)
Beginning Balance (in shares) at Dec. 31, 2012		199,225
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	79,809			79,809
Other Comprehensive Income (Loss)	(38,141)				(38,141)
Stock issued, including related tax benefits	4,675	1,544	(455)			3,586
Stock issued, including related tax benefits (in shares)		854
Stock-based compensation awards	3,207		3,207
Acquisition of treasury stock (in shares)	(6,400)	(6,421)
Acquisition of treasury stock	(71,337)					(71,337)
Common stock cash dividends	(31,137)			(31,137)
Ending Balance at Jun. 30, 2013	$ 2,028,732	$ 543,637	$ 1,429,019	$ 412,609	$ (32,466)	$ (324,067)
Ending Balance (in shares) at Jun. 30, 2013		193,658