Consolidated Statements of Changes in Stockholders' Equity (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, 2009	$ 837,663	$ 122,679	$ 257,643	$ 454,343	$ 2,998
Balance, shares at Dec. 31, 2009		36,840,453
Net income	52,206			52,206
Other comprehensive income	(3,617)				(3,617)
Comprehensive income	48,589
Cash dividends declared ($0.96 per common share)	(35,721)			(35,721)
Common stock activity, long-term incentive plan, including excess income tax benefit	6,017	176	5,841
Common stock activity, long-term incentive plan, including excess income tax benefit, Shares		52,823
Balance at Dec. 31, 2010	856,548	122,855	263,484	470,828	(619)
Balance, shares at Dec. 31, 2010		36,893,276
Net income	76,759			76,759
Other comprehensive income	(25,891)				(25,891)
Comprehensive income	50,868
Cash dividends declared ($0.96 per common share)	(70,617)			(70,617)
Common stock issued in stock offering	213,994	23,170	190,824
Common stock issued in stock offering, Shares		6,958,143
Common stock issued in business combination	1,308,044	135,845	1,172,199
Common stock issued in business combination, Shares		40,794,261
Common stock activity, long-term incentive plan, including excess income tax benefit	8,326	199	8,127
Common stock activity, long-term incentive plan, including excess income tax benefit, Shares		59,816
Balance at Dec. 31, 2011	2,367,163	282,069	1,634,634	476,970	(26,510)
Balance, shares at Dec. 31, 2011		84,705,496
Net income	151,742			151,742
Other comprehensive income	3,585				3,585
Comprehensive income	155,327
Cash dividends declared ($0.96 per common share)	(82,690)			(82,690)
Common stock activity, long-term incentive plan, including excess income tax benefit	13,478	474	13,004
Common stock activity, long-term incentive plan, including excess income tax benefit, Shares		142,300
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