Consolidated Statements of Changes in Stockholders Equity (Unaudited) (USD $) In Thousands, except Share data	Total	Common Stock [Member]	Capital Surplus [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss), net [Member]
Balance, at Dec. 31, 2012	$ 2,453,278	$ 282,543	$ 1,647,638	$ 546,022	$ (22,925)
Balance, Shares at Dec. 31, 2012		84,847,796
Net income	128,640			128,640
Other comprehensive income	(61,846)				(61,846)
Comprehensive income	66,794			128,640	(61,846)
Cash dividends declared ($0.72 per common share)	(61,000)			(61,000)
Common stock activity, long-term incentive plan	12,370	256	12,114
Common stock activity, long-term incentive plan, shares		76,801
Purchase of common stock	(115,000)	(9,383)	(105,617)
Purchase of common stock, shares		(2,817,640)
Balance at Sep. 30, 2013	2,356,442	273,416	1,554,135	613,662	(84,771)
Balance, Shares at Sep. 30, 2013		82,106,957
Balance, at Dec. 31, 2013	2,425,069	273,850	1,558,432	628,166	(35,379)
Balance, Shares at Dec. 31, 2013		82,237,162
Net income	135,630			135,630
Other comprehensive income	8,686				8,686
Comprehensive income	144,316			135,630	8,686
Cash dividends declared ($0.72 per common share)	(60,290)			(60,290)
Common stock activity, long-term incentive plan	10,214	749	9,465
Common stock activity, long-term incentive plan, shares		224,963
Purchase of common stock	(9,967)	(2,982)	(6,985)
Purchase of common stock, shares		(895,485)
Balance at Sep. 30, 2014	$ 2,509,342	$ 271,617	$ 1,560,912	$ 703,506	$ (26,693)
Balance, Shares at Sep. 30, 2014		81,566,640