Loans Receivable and Related Allowance for Loan Losses - Loan Portfolio by Internal Risk Rating System (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	$ 593,376	$ 583,361
Not Rated
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	337,912	329,119
Pass
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	241,117	239,420
Special Mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	4,065	3,221
Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	10,282	11,601
Doubtful
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	0	0
Residential first mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	230,504	221,823
Residential first mortgages | Not Rated
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	229,401	220,730
Residential first mortgages | Pass
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	0	0
Residential first mortgages | Special Mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	0	0
Residential first mortgages | Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	1,103	1,093
Residential first mortgages | Doubtful
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	0	0
Home equity loans and lines of credit
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	100,454	99,940
Home equity loans and lines of credit | Not Rated
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	99,474	98,946
Home equity loans and lines of credit | Pass
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	0	0
Home equity loans and lines of credit | Special Mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	0	0
Home equity loans and lines of credit | Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	980	994
Home equity loans and lines of credit | Doubtful
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	0	0
Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	198,602	193,068
Commercial real estate | Not Rated
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	0	0
Commercial real estate | Pass
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	187,762	182,460
Commercial real estate | Special Mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	3,831	2,744
Commercial real estate | Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	7,009	7,864
Commercial real estate | Doubtful
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	0	0
Commercial Business
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	54,693	58,941
Commercial Business | Not Rated
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	0	0
Commercial Business | Pass
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	53,355	56,960
Commercial Business | Special Mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	234	477
Commercial Business | Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	1,104	1,504
Commercial Business | Doubtful
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	0	0
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	9,123	9,589
Consumer | Not Rated
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	9,037	9,443
Consumer | Pass
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	0	0
Consumer | Special Mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	0	0
Consumer | Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	86	146
Consumer | Doubtful
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	$ 0	$ 0