Investment Securities Available for Sale - Summary of Ratings by Segment of Investment Securities Available for Sale (Detail)	Sep. 30, 2012
State and municipal [Member]
Available For Sale Securities By Credit Quality Indicator [Line Items]
Available for securities fair value moodys credit rating	100.00%
State and municipal [Member] | Moody's Aa1 - A1 Rating [Member]
Available For Sale Securities By Credit Quality Indicator [Line Items]
Available for securities fair value moodys credit rating	75.00%
State and municipal [Member] | Moody's Baa2 Rating [Member]
Available For Sale Securities By Credit Quality Indicator [Line Items]
Available for securities fair value moodys credit rating	12.00%
State and municipal [Member] | Not Rated [Member]
Available For Sale Securities By Credit Quality Indicator [Line Items]
Available for securities fair value moodys credit rating	13.00%
Collateralized mortgage obligations [Member]
Available For Sale Securities By Credit Quality Indicator [Line Items]
Available for securities fair value moodys credit rating	100.00%
Collateralized mortgage obligations [Member] | Moody's Aaa Rating [Member]
Available For Sale Securities By Credit Quality Indicator [Line Items]
Available for securities fair value moodys 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 moodys credit rating	100.00%
Other mortgage-backed (federal agencies) [Member] | Moody's Aaa Rating [Member]
Available For Sale Securities By Credit Quality Indicator [Line Items]
Available for securities fair value moodys 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 moodys credit rating	100.00%
SBA loan-backed (federal agency) [Member] | Moody's Aaa Rating [Member]
Available For Sale Securities By Credit Quality Indicator [Line Items]
Available for securities fair value moodys credit rating	100.00%