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, 2010	$ 1,880,389	$ 538,492	$ 1,420,127	$ 158,453	$ 12,495	$ (249,178)
Beginning Balance (in shares) at Dec. 31, 2010		199,050
Comprehensive income:
Net Income	33,785			33,785
Other comprehensive income	2,354				2,354
Stock issued, including related tax benefits	1,231	177	(8)			1,062
Stock issued, including related tax benefits (in shares)		141
Stock-based compensation awards	547		547
Common stock cash dividends	(7,984)			(7,984)
Ending Balance at Mar. 31, 2011	1,910,322	538,669	1,420,666	184,254	14,849	(248,116)
Ending Balance (in shares) at Mar. 31, 2011		199,191
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
Comprehensive income:
Net Income	38,132			38,132
Other comprehensive income	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