Securities - Held to Maturity with Unrealized Losses (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012
Schedule of Held-to-maturity Securities [Line Items]
Held to maturity securities, Losses less than 12 months, Fair Value	$ 87,852
Held to maturity securities, Losses Less than 12 months, Gross Unrealized Losses	259
Held to maturity securities, Losses 12 months or longer, Fair value	54,445
Held to maturity securities, Losses 12 months or longer, Gross Unrealized Losses	682
Held to maturity securities, Total, Fair value	142,297
Held to maturity securities, Total, Gross Unrealized Losses	941
Municipal Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held to maturity securities, Losses less than 12 months, Fair Value
Held to maturity securities, Losses Less than 12 months, Gross Unrealized Losses
Held to maturity securities, Losses 12 months or longer, Fair value
Held to maturity securities, Losses 12 months or longer, Gross Unrealized Losses
Held to maturity securities, Total, Fair value
Held to maturity securities, Total, Gross Unrealized Losses
Mortgage-backed securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held to maturity securities, Losses less than 12 months, Fair Value
Held to maturity securities, Losses Less than 12 months, Gross Unrealized Losses
Held to maturity securities, Losses 12 months or longer, Fair value
Held to maturity securities, Losses 12 months or longer, Gross Unrealized Losses
Held to maturity securities, Total, Fair value
Held to maturity securities, Total, Gross Unrealized Losses
CMOs [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held to maturity securities, Losses less than 12 months, Fair Value	87,852
Held to maturity securities, Losses Less than 12 months, Gross Unrealized Losses	259
Held to maturity securities, Losses 12 months or longer, Fair value	54,445
Held to maturity securities, Losses 12 months or longer, Gross Unrealized Losses	682
Held to maturity securities, Total, Fair value	142,297
Held to maturity securities, Total, Gross Unrealized Losses	$ 941