Loans Receivable and Related Allowance for Loan Losses - Loan Portfolio by Internal Risk Rating System (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	$ 590,177	$ 583,361
Not Rated
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	332,131	329,119
Pass
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	242,427	239,420
Special Mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	4,587	3,221
Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	11,032	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	224,690	221,823
Residential first mortgages | Not Rated
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	223,500	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	1,190	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	100,241	99,940
Home equity loans and lines of credit | Not Rated
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	99,447	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	794	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	196,788	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	185,187	182,460
Commercial real estate | Special Mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	4,193	2,744
Commercial real estate | Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	7,408	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	59,200	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	57,240	56,960
Commercial Business | Special Mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	394	477
Commercial Business | Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	1,566	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	9,258	9,589
Consumer | Not Rated
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	9,184	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	74	146
Consumer | Doubtful
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	$ 0	$ 0