Fair Value Measurement - Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale securities, Fair value	$ 492,412	$ 499,790
Fair Value, Measurements, Recurring [Member] | Interest Rate Caps [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale securities, Fair value	126	180
Fair Value, Measurements, Recurring [Member] | US Treasury and Government Sponsored Entities Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale securities, Fair value	226,893	227,957
Fair Value, Measurements, Recurring [Member] | Mortgage-Backed GSE Securities: Residential [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale securities, Fair value	265,519	271,833
Fair Value, Measurements, Recurring [Member] | Loans Held For Sale, at Fair Value [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale securities, Fair value	1,608
Fair Value, Measurements, Recurring [Member] | Purchased Certificate of Deposit Option [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale securities, Fair value	935	930
Fair Value, Measurements, Recurring [Member] | Written Certificate of Deposit Option [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Liabilities, Fair value	935	930
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | US Treasury and Government Sponsored Entities Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale securities, Fair value	226,893	227,957
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Mortgage-Backed GSE Securities: Residential [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale securities, Fair value	265,519	271,833
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Purchased Certificate of Deposit Option [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale securities, Fair value	935	930
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Written Certificate of Deposit Option [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Liabilities, Fair value	935	930
Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Interest Rate Caps [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale securities, Fair value	126	180
Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Loans Held For Sale, at Fair Value [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale securities, Fair value	$ 1,608