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	38,132			38,132
Other Comprehensive Income (Loss)	4,154				4,154
Stock issued, including related tax benefits	1,365	208	(565)			1,722
Stock issued, including related tax benefits (in shares)		190
Stock-based compensation awards	713		713
Common stock cash dividends	(14,040)			(14,040)
Ending Balance at Mar. 31, 2012	2,022,863	540,594	1,423,875	288,151	12,109	(241,866)
Ending Balance (in shares) at Mar. 31, 2012		200,354
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	39,227			39,227
Other Comprehensive Income (Loss)	(38)				(38)
Stock issued, including related tax benefits	2,735	393	196			2,146
Stock issued, including related tax benefits (in shares)		297
Stock-based compensation awards	847		847
Acquisition of treasury stock (in shares)	(4,200)	(4,246)
Acquisition of treasury stock	(47,046)					(47,046)
Common stock cash dividends	(15,618)			(15,618)
Ending Balance at Mar. 31, 2013	$ 2,061,763	$ 542,486	$ 1,427,310	$ 387,546	$ 5,637	$ (301,216)
Ending Balance (in shares) at Mar. 31, 2013		195,276