Fair Value Measurement - Assets and Liabilities Measured on Non-recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Commercial Loans [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Impaired loans	$ 3,828	$ 3,803
Commercial Loans [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Impaired loans	3,828	3,803
Residential Loans [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Impaired loans	406	765
Residential Loans [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Impaired loans	406	765
Consumer Loans [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Impaired loans	276	260
Consumer Loans [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Impaired loans	276	260
Mortgage Servicing Rights [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Impaired loans	1,457	1,138
Mortgage Servicing Rights [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Impaired loans	1,457	1,138
Permanent Real Estate Loans [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Other real estate owned, net	626	640
Permanent Real Estate Loans [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Other real estate owned, net	626	640
Construction Loans [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Other real estate owned, net	1,013	1,286
Construction Loans [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Other real estate owned, net	$ 1,013	$ 1,286