Parent Company (Details 2) (USD $) In Thousands, unless otherwise specified	0 Months Ended	3 Months Ended															12 Months Ended
	May 27, 2009	Dec. 31, 2011	Sep. 30, 2011		Jun. 30, 2011		Mar. 31, 2011		Dec. 31, 2010		Sep. 30, 2010		Jun. 30, 2010		Mar. 31, 2010		Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Operating activities:
Net income		$ 30,496	$ 31,737	[1]	$ 29,763	[1]	$ 27,560	[1]	$ 27,030	[1]	$ 28,996	[1]	$ 31,493	[1]	$ 15,390	[1]	$ 119,558	$ 102,909	$ 82,170
Adjustments to reconcile net income to net cash provided by operating activities
NET CASH PROVIDED BY OPERATING ACTIVITIES																	149,335	146,876	89,935
Investing activities:
NET CASH PROVIDED (USED) BY INVESTING ACTIVITIES																	(353,317)	1,351,109	493,711
Financing activities:
Proceeds from issuance of preferred stock																	0	0	125,000
Repurchase of preferred stock																	0	0	(125,000)
Repurchase of common stock warrant	(5,000)																0	0	(5,025)
Proceeds from issuance of common stock																	0	400,018	79,526
Cash dividends - preferred																	0	0	(1,789)
Cash dividends-common stock																	(69,255)	(65,634)	(63,891)
NET CASH (USED) PROVIDED BY FINANCING ACTIVITIES																	58,188	(1,135,905)	(601,019)
Increase (decrease) in cash and cash equivalents																	(145,794)	362,080	(17,373)
Cash and cash equivalents at beginning of period							523,113								161,033		523,113	161,033	178,406
Cash and cash equivalents at end of period		377,319							523,113								377,319	523,113	161,033
Parent [Member]
Operating activities:
Net income																	119,558	102,909	82,170
Adjustments to reconcile net income to net cash provided by operating activities
Equity in undistributed income of subsidiaries																	(52,973)	(86,807)	(56,893)
(Decrease) increase in Federal income tax payable																	(936)	(2,042)	3,893
Other																	571	(175)	(391)
NET CASH PROVIDED BY OPERATING ACTIVITIES																	66,220	13,885	28,779
Investing activities:
Loans to subsidiaries																	(18,704)	(242,327)	(318,000)
Repayment of loans to subsidiaries																	76,030	313,550	293,000
Payments for investments in and advances to subsidiaries																	0	(381,600)	(350)
Purchases of investment securities																	(45)	(45)	(46)
NET CASH PROVIDED (USED) BY INVESTING ACTIVITIES																	57,281	(310,422)	(25,396)
Financing activities:
Repayment of short-term borrowings																	0	(52,393)	(47)
Proceeds from issuance of preferred stock																	0	0	125,000
Repurchase of preferred stock																	0	0	(125,000)
Repurchase of common stock warrant																	0	0	(5,025)
Proceeds from issuance of common stock																	0	400,018	79,526
Cash dividends - preferred																	0	0	(1,789)
Cash dividends-common stock																	(69,255)	(65,634)	(63,891)
Proceeds from exercise of stock options																	0	826	2,936
Purchase of treasury shares																	(2,295)	(2,634)	(1,758)
NET CASH (USED) PROVIDED BY FINANCING ACTIVITIES																	(71,550)	280,183	9,952
Increase (decrease) in cash and cash equivalents																	51,951	(16,354)	13,335
Cash and cash equivalents at beginning of period							9,648								26,002		9,648	26,002	12,667
Cash and cash equivalents at end of period		$ 61,599							$ 9,648								$ 61,599	$ 9,648	$ 26,002

[1] * Net income restated to reflect purchase accounting adjustments which decreased the bargain purchase gain recognized on the George Washington acquisition to $1.0 million in the quarter ended March 31, 2010.