Loans Receivable and Related Allowance for Loan Losses - Classes of Loan Portfolio by Aging Categories (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Loans Not Past Due	$ 574,298	$ 514,279
Nonperforming, Non Accrual	3,003	3,278
Total Loans	583,361	520,980
30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Loans Past Due	3,907	3,021
Nonperforming, Non Accrual	0	77
60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Loans Past Due	1,463	358
Nonperforming, Non Accrual	75	557
90 Days and Greater Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Loans Past Due	690	44
Nonperforming, Non Accrual	1,644	1,544
Residential first mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Loans Not Past Due	218,515	194,830
Nonperforming, Non Accrual	856	1,126
Total Loans	221,823	198,167
Residential first mortgages | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Loans Past Due	1,936	1,916
Nonperforming, Non Accrual	0	77
Residential first mortgages | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Loans Past Due	357	295
Nonperforming, Non Accrual	75	0
Residential first mortgages | 90 Days and Greater Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Loans Past Due	159	0
Nonperforming, Non Accrual	415	977
Home equity loans and lines of credit
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Loans Not Past Due	98,112	90,557
Nonperforming, Non Accrual	526	340
Total Loans	99,940	91,359
Home equity loans and lines of credit | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Loans Past Due	598	460
Nonperforming, Non Accrual	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	370	0
Nonperforming, Non Accrual	0	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	334	2
Nonperforming, Non Accrual	518	340
Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Loans Not Past Due	190,451	165,318
Nonperforming, Non Accrual	964	1,073
Total Loans	193,068	166,994
Commercial real estate | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Loans Past Due	1,026	561
Nonperforming, Non Accrual	0	0
Commercial real estate | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Loans Past Due	430	0
Nonperforming, Non Accrual	0	557
Commercial real estate | 90 Days and Greater Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Loans Past Due	197	42
Nonperforming, Non Accrual	623	119
Commercial business
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Loans Not Past Due	58,058	56,972
Nonperforming, Non Accrual	584	726
Total Loans	58,941	57,788
Commercial business | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Loans Past Due	74	56
Nonperforming, Non Accrual	0	0
Commercial business | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Loans Past Due	225	34
Nonperforming, Non Accrual	0	0
Commercial business | 90 Days and Greater Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Loans Past Due	0	0
Nonperforming, Non Accrual	15	95
Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Loans Not Past Due	9,162	6,602
Nonperforming, Non Accrual	73	13
Total Loans	9,589	6,672
Consumer | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Loans Past Due	273	28
Nonperforming, Non Accrual	0	0
Consumer | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Loans Past Due	81	29
Nonperforming, Non Accrual	0	0
Consumer | 90 Days and Greater Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Loans Past Due	0	0
Nonperforming, Non Accrual	$ 73	$ 13