Fair Value Measurement - Assets and Liabilities Measured at Fair Value on Non-recurring Basis (Detail) - USD ($)	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016
Mortgage Servicing Rights [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Mortgage servicing rights	$ 87,000		$ 2,800,000
Fair Value, Measurements, Nonrecurring [Member] | Multifamily [Member] | Commercial Loans [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Impaired loans	418,000
Fair Value, Measurements, Nonrecurring [Member] | Home Equity [Member] | Consumer Loans [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Impaired loans	28,000	$ 228,000
Fair Value, Measurements, Nonrecurring [Member] | Auto [Member] | Consumer Loans [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Impaired loans	17,000	177,000
Fair Value, Measurements, Nonrecurring [Member] | Marine [Member] | Consumer Loans [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Impaired loans	169,000
Fair Value, Measurements, Nonrecurring [Member] | Recreational Vehicle [Member] | Consumer Loans [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Impaired loans	55,000	89,000
Fair Value, Measurements, Nonrecurring [Member] | Mortgage Servicing Rights [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Mortgage servicing rights	82,000
Fair Value, Measurements, Nonrecurring [Member] | Construction [Member] | Commercial Loans [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Other real estate owned, net	448,000	748,000
Fair Value, Measurements, Nonrecurring [Member] | Nonresidential [Member] | Commercial Loans [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Impaired loans		2,257,000
Fair Value, Measurements, Nonrecurring [Member] | Secured [Member] | Commercial Loans [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Impaired loans		284,000
Residential Mortgage Loans [Member] | Fair Value, Measurements, Nonrecurring [Member] | One-to Four-Family [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Impaired loans	756,000	919,000
Other real estate owned, net	35,000	281,000
Significant Other Observable Inputs (Level 2) [Member] | Fair Value, Measurements, Nonrecurring [Member] | Mortgage Servicing Rights [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Mortgage servicing rights	82,000
Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Nonrecurring [Member] | Multifamily [Member] | Commercial Loans [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Impaired loans	418,000
Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Nonrecurring [Member] | Home Equity [Member] | Consumer Loans [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Impaired loans	28,000	228,000
Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Nonrecurring [Member] | Auto [Member] | Consumer Loans [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Impaired loans	17,000	177,000
Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Nonrecurring [Member] | Marine [Member] | Consumer Loans [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Impaired loans	169,000
Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Nonrecurring [Member] | Recreational Vehicle [Member] | Consumer Loans [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Impaired loans	55,000	89,000
Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Nonrecurring [Member] | Construction [Member] | Commercial Loans [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Other real estate owned, net	448,000	748,000
Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Nonrecurring [Member] | Nonresidential [Member] | Commercial Loans [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Impaired loans		2,257,000
Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Nonrecurring [Member] | Secured [Member] | Commercial Loans [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Impaired loans		284,000
Significant Unobservable Inputs (Level 3) [Member] | Residential Mortgage Loans [Member] | Fair Value, Measurements, Nonrecurring [Member] | One-to Four-Family [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Impaired loans	756,000	919,000
Other real estate owned, net	$ 35,000	$ 281,000