Investment Securities Available for Sale - Summary of Ratings by Standards Poors of Investment Securities Available for Sale (Detail)	Dec. 31, 2012
State and municipal [Member]
Available For Sale Securities By Credit Quality Indicator [Line Items]
Available for securities fair value standard & poors credit rating	100.00%
State and municipal [Member] | Standard and Poor's Aa - Aa- Rating [Member]
Available For Sale Securities By Credit Quality Indicator [Line Items]
Available for securities fair value standard & poors credit rating	41.00%
State and municipal [Member] | Not Rated [Member]
Available For Sale Securities By Credit Quality Indicator [Line Items]
Available for securities fair value standard & poors credit rating	59.00%
Collateralized mortgage obligations (federal agencies) [Member]
Available For Sale Securities By Credit Quality Indicator [Line Items]
Available for securities fair value standard & poors credit rating	100.00%
Collateralized mortgage obligations (federal agencies) [Member] | Standard & Poor's, Aa+ Rating [Member]
Available For Sale Securities By Credit Quality Indicator [Line Items]
Available for securities fair value standard & poors credit rating	100.00%
Other mortgage-backed (federal agencies) [Member]
Available For Sale Securities By Credit Quality Indicator [Line Items]
Available for securities fair value standard & poors credit rating	100.00%
Other mortgage-backed (federal agencies) [Member] | Standard & Poor's, Aa+ Rating [Member]
Available For Sale Securities By Credit Quality Indicator [Line Items]
Available for securities fair value standard & poors credit rating	100.00%
SBA Loan-Backed (Federal Agency) [Member]
Available For Sale Securities By Credit Quality Indicator [Line Items]
Available for securities fair value standard & poors credit rating	100.00%
SBA Loan-Backed (Federal Agency) [Member] | Standard & Poor's, Aa+ Rating [Member]
Available For Sale Securities By Credit Quality Indicator [Line Items]
Available for securities fair value standard & poors credit rating	100.00%