Securities - Held to Maturity with Unrealized Losses (Detail) (USD $)	Sep. 30, 2012
Held to maturity securities, Losses less than 12 months, Fair Value	$ 310,442
Held to maturity securities, Losses Less than 12 months, Gross Unrealized Losses	752
Held to maturity securities, Losses 12 months or longer, Fair value	74,499
Held to maturity securities, Losses 12 months or longer, Gross Unrealized Losses	959
Held to maturity securities, Total, Fair value	384,941
Held to maturity securities, Total, Gross Unrealized Losses	1,711
Municipal obligations [Member]
Held to maturity securities, Losses less than 12 months, Fair Value	1,862
Held to maturity securities, Losses Less than 12 months, Gross Unrealized Losses	5
Held to maturity securities, Total, Fair value	1,862
Held to maturity securities, Total, Gross Unrealized Losses	5
Mortgage-backed securities [Member]
Held to maturity securities, Losses less than 12 months, Fair Value	308,580
Held to maturity securities, Losses Less than 12 months, Gross Unrealized Losses	747
Held to maturity securities, Losses 12 months or longer, Fair value	74,499
Held to maturity securities, Losses 12 months or longer, Gross Unrealized Losses	959
Held to maturity securities, Total, Fair value	383,079
Held to maturity securities, Total, Gross Unrealized Losses	$ 1,706