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, 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)		(4,246)
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
Beginning Balance at Dec. 31, 2013	2,063,187	544,568	1,432,974	463,843	(37,341)	(340,857)
Beginning Balance (in shares) at Dec. 31, 2013		192,652
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	41,783			41,783
Other Comprehensive Income (Loss)	15,452				15,452
Stock issued, including related tax benefits	2,177	253	539			1,385
Stock issued, including related tax benefits (in shares)		198
Stock-based compensation awards	1,033		1,033
Acquisition of treasury stock (in shares)		(4,000)
Acquisition of treasury stock	(49,804)					(49,804)
Common stock cash dividends	(15,109)			(15,109)
Ending Balance at Mar. 31, 2014	$ 2,058,719	$ 544,821	$ 1,434,546	$ 490,517	$ (21,889)	$ (389,276)
Ending Balance (in shares) at Mar. 31, 2014		188,850