Loans Receivable and Related Allowance for Loan Losses - Loan Portfolio by Internal Risk Rating System (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	$ 583,361	$ 520,980
Not Rated
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	329,119	294,717
Pass
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	239,420	213,437
Special Mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	3,221	6,003
Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	11,601	6,823
Doubtful
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	0	0
Residential first mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	221,823	198,167
Residential first mortgages | Not Rated
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	220,730	197,041
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	1,093	1,126
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	99,940	91,359
Home equity loans and lines of credit | Not Rated
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	98,946	91,017
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	994	342
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	193,068	166,994
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	182,460	161,312
Commercial real estate | Special Mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	2,744	1,077
Commercial real estate | Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	7,864	4,605
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	58,941	57,788
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	56,960	52,125
Commercial Business | Special Mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	477	4,926
Commercial Business | Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	1,504	737
Commercial Business | Doubtful
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	0	0
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	9,589	6,672
Consumer | Not Rated
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	9,443	6,659
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	146	13
Consumer | Doubtful
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	$ 0	$ 0