Loans - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2016 USD ($) TDR	Dec. 31, 2015 USD ($) TDR Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Servicing loans for participants	$ 6,197,000	$ 7,347,000
Loans past due 90 days or more	0	$ 0
Impaired loans, additional funds committed	0
Number of loans modified | Loan		2
Aggregate balance of loans modified		$ 434,000
Troubled debt restructuring amount	0
Allowances related to troubled debt restructurings	$ 200,000	284,000
Minimum past due days for loan rating	90 days
Total loans	$ 335,086,000	287,102,000
Residential Mortgage [Member] | Substandard [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	890,000	378,000
Residential Mortgage [Member] | Special Mention [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	1,471,000	2,262,000
Home Equity Loans and Lines of Credit [Member] | Special Mention [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	400,000	277,000
30 - 59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Troubled debt restructurings defaulted over 30 days past due	$ 0	$ 0
Minimum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest rate on modified loans, deduction range		1.00%
Maximum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest rate on modified loans, deduction range		3.00%
Residential Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans subject to troubled debt restructurings | TDR	13	12
Loans subject to troubled debt restructurings, amount	$ 2,809,000	$ 2,938,000
Residential Real Estate [Member] | Minimum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Troubled debt restructuring, interest rate concession period	3 months
Residential Real Estate [Member] | Maximum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Troubled debt restructuring, interest rate concession period	30 years
Commercial Real Estate Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans subject to troubled debt restructurings | TDR	3	5
Loans subject to troubled debt restructurings, amount	$ 624,000	$ 1,234,000
Total loans	88,394,000	74,911,000
Commercial Real Estate Loans [Member] | Substandard [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 208,000	249,000
Commercial Real Estate Loans [Member] | Special Mention [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans		$ 1,145,000
Commercial Real Estate Loans [Member] | Maximum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Troubled debt restructuring, interest rate concession period	1 year