Fair Value Measurement - Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Available for sale securities, Fair value	$ 542,811	$ 574,562
Fair Value, Measurements, Recurring [Member] | US Treasury and Government Sponsored Entities Securities [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Available for sale securities, Fair value	229,763	163,692
Fair Value, Measurements, Recurring [Member] | Equity Securities [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Available for sale securities, Fair value	396	313
Fair Value, Measurements, Recurring [Member] | Mortgage-Backed GSE Securities: Residential [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Available for sale securities, Fair value	312,652	410,557
Fair Value, Measurements, Recurring [Member] | Interest Rate Cap [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Available for sale securities, Fair value	594	436
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Fair Value, Measurements, Recurring [Member] | US Treasury and Government Sponsored Entities Securities [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Available for sale securities, Fair value
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Fair Value, Measurements, Recurring [Member] | Equity Securities [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Available for sale securities, Fair value	396	313
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Fair Value, Measurements, Recurring [Member] | Mortgage-Backed GSE Securities: Residential [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Available for sale securities, Fair value
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Fair Value, Measurements, Recurring [Member] | Interest Rate Cap [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Available for sale securities, Fair value
Significant Other Observable Inputs (Level 2) [Member] | Fair Value, Measurements, Recurring [Member] | US Treasury and Government Sponsored Entities Securities [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Available for sale securities, Fair value	229,763	163,692
Significant Other Observable Inputs (Level 2) [Member] | Fair Value, Measurements, Recurring [Member] | Equity Securities [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Available for sale securities, Fair value
Significant Other Observable Inputs (Level 2) [Member] | Fair Value, Measurements, Recurring [Member] | Mortgage-Backed GSE Securities: Residential [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Available for sale securities, Fair value	312,652	410,557
Significant Other Observable Inputs (Level 2) [Member] | Fair Value, Measurements, Recurring [Member] | Interest Rate Cap [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Available for sale securities, Fair value
Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Recurring [Member] | US Treasury and Government Sponsored Entities Securities [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Available for sale securities, Fair value
Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Recurring [Member] | Equity Securities [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Available for sale securities, Fair value
Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Recurring [Member] | Mortgage-Backed GSE Securities: Residential [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Available for sale securities, Fair value
Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Recurring [Member] | Interest Rate Cap [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Available for sale securities, Fair value	$ 594	$ 436