Summary of Significant Accounting Policies and Recent Accounting Pronouncements - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Summary Of Significant Accounting Policies And Recent Accounting Pronouncements [Line Items]
Number of wholly-owned bank subsidiaries	2
Maximum refinement period of fair values after closing date of an acquisition	1 year
Specific reserve balances to include all commercial, commercial real estate and substandard mortgage loans	$500,000 or greater
Building [Member]
Summary Of Significant Accounting Policies And Recent Accounting Pronouncements [Line Items]
Estimated useful lives of the assets	39 years
Furniture, fixtures and equipment [Member] | Minimum [Member]
Summary Of Significant Accounting Policies And Recent Accounting Pronouncements [Line Items]
Estimated useful lives of the assets	3 years
Furniture, fixtures and equipment [Member] | Maximum [Member]
Summary Of Significant Accounting Policies And Recent Accounting Pronouncements [Line Items]
Estimated useful lives of the assets	7 years
Software [Member]
Summary Of Significant Accounting Policies And Recent Accounting Pronouncements [Line Items]
Amortization expense charged off period	3 years
Property and Equipment [Member]
Summary Of Significant Accounting Policies And Recent Accounting Pronouncements [Line Items]
Impairment loss	$ 0	$ 0	$ 0