Consolidated Statements Of Changes In Shareholders Equity (Unaudited) (USD $) In Thousands, unless otherwise specified	Total	Series C Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member] Series C Preferred Stock [Member]	Common Stock [Member]	Common Stock [Member] Series C Preferred Stock [Member]	Surplus [Member]	Surplus [Member] Series C Preferred Stock [Member]	Treasury Stock [Member]	Treasury Stock [Member] Series C Preferred Stock [Member]	Retained Earnings [Member]	Retained Earnings [Member] Series C Preferred Stock [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Accumulated Other Comprehensive Income (Loss) [Member] Series C Preferred Stock [Member]
Balance at Dec. 31, 2010	$ 1,436,549		$ 49,640		$ 34,864		$ 965,203		$ 0		$ 392,354		$ (5,512)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	58,354										58,354
Other comprehensive income, net of tax	8,983												8,983
Cash dividends declared on common stock	(6,344)										(6,344)
Dividends on preferred stock	(3,000)										(3,000)
Accretion on preferred stock	0		96								(96)
Common stock repurchases	(68)								(68)
Stock-based compensation	3,433						3,433
Common stock issued for:
Acquisitions	26,486				883		25,603
Exercise of stock options and warrants	681				49		632
Restricted stock awards	(3)				38		(41)
Employee stock purchase plan	2,055				67		1,988
Director compensation plan	1,061				25		1,036
Balance at Sep. 30, 2011	1,528,187		49,736		35,926		997,854		(68)		441,268		3,471
Balance at Dec. 31, 2011	1,543,533		49,768		35,982		1,001,316		(112)		459,457		(2,878)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	81,107										81,107		0
Other comprehensive income, net of tax	12,683												12,683
Cash dividends declared on common stock	(6,537)										(6,537)
Dividends on preferred stock	(6,374)										(6,374)
Accretion on preferred stock	0		103								(103)
Stock-based compensation	7,260						7,260
Issuance of Series C preferred stock		122,690		126,500				(3,810)
Common stock issued for:
Acquisitions	894				26		868
Exercise of stock options and warrants	4,098				439		10,050		(6,391)
Restricted stock awards	(1,016)				123		(152)		(987)
Employee stock purchase plan	1,832				55		1,777
Director compensation plan	1,130				22		1,108
Balance at Sep. 30, 2012	$ 1,761,300		$ 176,371		$ 36,647		$ 1,018,417		$ (7,490)		$ 527,550		$ 9,805