Mergers and Acquisitions - Schedule of Acquired Identifiable Assets and Liabilities Assumed (Detail) (USD $) In Thousands, unless otherwise specified			0 Months Ended	6 Months Ended		0 Months Ended
	Jun. 30, 2014	Dec. 31, 2013	Jan. 31, 2014 Virginia Commerce Bancorp, Inc. [Member]	Jun. 30, 2014 Virginia Commerce Bancorp, Inc. [Member]	Jan. 31, 2014 Virginia Commerce Bancorp, Inc. [Member]	Jan. 31, 2014 Virginia Commerce Bancorp, Inc. [Member] Core Deposit Intangible Assets [Member]
Business Acquisition [Line Items]
Value of common shares issued (18,330,347 shares)			$ 547,894
Fair value of stock options assumed			4,368	4,370
Cash to redeem the Treasury warrant				33,263	33,263
Cash for fractional shares			8
Total purchase price			585,533	8
Cash and cash equivalents					130,569
Investment securities					476,541
Loans					2,012,521
Premises and equipment					10,786
Core deposit intangibles						17,143
Other assets					106,244
Total identifiable assets					2,753,804
Deposits					2,024,969
Short-term borrowings					263,816
Long-term borrowings					204,335
Other liabilities					11,133
Total identifiable liabilities					2,504,253
Net assets acquired including identifiable intangible assets					249,551
Resulting goodwill	$ 710,165	$ 375,547		$ 335,980	$ 335,982