Available-for-Sale Securities Measured at Fair Value (Parenthetical) (Detail) (Maximum)	Sep. 30, 2011
U.S. Government and agency securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, maturities	2 years
Asset-backed securities and collateralized mortgage obligations
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, maturities	26 years