Mergers and Acquisitions - Additional Information (Detail) (USD $)	12 Months Ended	0 Months Ended
	Dec. 31, 2014	Jan. 31, 2014	Dec. 31, 2013
Business Acquisition [Line Items]
Outstanding common stock acquired		100.00%
Business acquisition date	Jan. 31, 2014
Total assets at consummation	$ 12,328,811,000		$ 8,735,324,000
Loans at consummation	9,119,492,000		6,713,599,000
Deposits at consummation	9,045,485,000		6,621,571,000
Contractually required principal and interest at acquisition		427,858,000
Expected cash flows at acquisition		189,277,000
Estimated fair value of acquired impaired loans at acquisition		179,199,000
Virginia Commerce Bancorp, Inc. [Member]
Business Acquisition [Line Items]
Total assets at consummation	2,769,716,000
Loans at consummation	2,065,490,000
Deposits at consummation	2,018,962,000
Common stock paid in cash	8,000	585,533,000
Stock options exchanged value	4,368,000
Cash paid cash to redeem the warrant	33,263,000
Goodwill arising from acquisition	335,644,000
Goodwill from acquisition expected to be tax deductible	0
Downward fair value adjustment on loans acquired	88,129,000
Downward fair value adjustment on real state properties	1,708,000
Premium on interest-bearing deposits acquired	6,007,000
Premium on term securities to purchase	3,700,000
Discount on junior subordinated debt securities acquired	16,384,000
Estimated remaining life of premium on interest-bearing deposits acquired	1 year
Estimated remaining life on premium of term securities to purchase	1 year 6 months 29 days
Estimated remaining life of discount on junior subordinated debt securities acquired	19 years 6 months 29 days
Assumed liabilities to provide severance benefits	109,000
Liabilities to provide severance benefits	0
Revenue since acquisition included in consolidated results	100,759,000
Revenue since acquisition included in consolidated results	44,856,000
Virginia Commerce Bancorp, Inc. [Member] | Common Stock [Member]
Business Acquisition [Line Items]
Common stock value	547,894,000
Number of shares issued in the transaction		18,330,347
Closing market price per common share		$ 29.89
Virginia Commerce Bancorp, Inc. [Member] | Core Deposit Intangible Assets [Member]
Business Acquisition [Line Items]
Purchase price allocation of Identifiable Intangible assets	$ 17,143,000
Estimated period of amortization of core deposit intangibles	10 years