Condensed Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013
Statement Of Cash Flows [Abstract]
NET CASH PROVIDED BY OPERATING ACTIVITIES	$ 57,520	$ 72,347
INVESTING ACTIVITIES
Proceeds from maturities and calls of securities held to maturity	176	1,029
Proceeds from sales of securities available for sale	81,194	5,821
Proceeds from maturities and calls of securities available for sale	354,689	398,962
Purchases of securities available for sale	(311,575)	(487,731)
Purchases of bank premises and equipment	(4,263)	(1,518)
Proceeds from sales of bank premises and equipment	11,426	197
Redemption of bank-owned life insurance policies	135	1,953
Purchases of other investment securities	(49,758)	(11,322)
Proceeds from sales and redemptions of other investment securities	33,329	4,559
Acquisition of Virginia Commerce Bancorp, Inc., net of cash paid	97,298	0
Net change in loans	(161,656)	(65,236)
NET CASH PROVIDED BY (USED IN) INVESTING ACTIVITIES	50,995	(153,286)
FINANCING ACTIVITIES
Cash dividends paid	(38,224)	(31,196)
Excess tax benefits from stock-based compensation arrangements	431	36
Acquisition of treasury stock	(1)	(91)
Proceeds from exercise of stock options	6,272	676
Repayment of long-term Federal Home Loan Bank borrowings	(420,732)	(210)
Proceeds from issuance of long-term Federal Home Loan Bank borrowings	700,000	0
Distribution of treasury stock for deferred compensation plan	79	69
Changes in:
Deposits	101,892	(174,980)
Federal funds purchased, securities sold under agreements to repurchase and other short-term borrowings	(159,473)	233,599
NET CASH PROVIDED BY FINANCING ACTIVITIES	190,244	27,903
Increase (Decrease) in cash and cash equivalents	298,759	(53,036)
Cash and cash equivalents at beginning of year	416,617	432,077
Cash and cash equivalents at end of period	$ 715,376	$ 379,041