Loans Receivable and Related Allowance for Loan Losses - Classes of Loan Portfolio by Aging Categories (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Loans Not Past Due	$ 586,335	$ 574,298
Nonaccrual	1,920	3,003
Total loans	593,376	583,361
30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Loans Past Due	3,482	3,907
Nonaccrual	0	0
60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Loans Past Due	1,073	1,463
Nonaccrual	83	75
90 Days and Greater Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Loans Past Due	566	690
Nonaccrual	1,233	1,644
Residential first mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Loans Not Past Due	227,774	218,515
Nonaccrual	967	856
Total loans	230,504	221,823
Residential first mortgages | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Loans Past Due	1,264	1,936
Nonaccrual	0	0
Residential first mortgages | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Loans Past Due	440	357
Nonaccrual	74	75
Residential first mortgages | 90 Days and Greater Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Loans Past Due	59	159
Nonaccrual	540	415
Home equity loans and lines of credit
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Loans Not Past Due	98,592	98,112
Nonaccrual	542	526
Total loans	100,454	99,940
Home equity loans and lines of credit | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Loans Past Due	753	598
Nonaccrual	0	0
Home equity loans and lines of credit | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Loans Past Due	244	370
Nonaccrual	9	0
Home equity loans and lines of credit | 90 Days and Greater Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Loans Past Due	323	334
Nonaccrual	526	518
Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Loans Not Past Due	196,655	190,451
Nonaccrual	309	964
Total loans	198,602	193,068
Commercial real estate | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Loans Past Due	1,111	1,026
Nonaccrual	0	0
Commercial real estate | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Loans Past Due	343	430
Nonaccrual	0	0
Commercial real estate | 90 Days and Greater Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Loans Past Due	184	197
Nonaccrual	104	623
Commercial business
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Loans Not Past Due	54,654	58,058
Nonaccrual	39	584
Total loans	54,693	58,941
Commercial business | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Loans Past Due	0	74
Nonaccrual	0	0
Commercial business | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Loans Past Due	0	225
Nonaccrual	0	0
Commercial business | 90 Days and Greater Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Loans Past Due	0	0
Nonaccrual	0	15
Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Loans Not Past Due	8,660	9,162
Nonaccrual	63	73
Total loans	9,123	9,589
Consumer | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Loans Past Due	354	273
Nonaccrual	0	0
Consumer | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Loans Past Due	46	81
Nonaccrual	0	0
Consumer | 90 Days and Greater Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Loans Past Due	0	0
Nonaccrual	$ 63	$ 73