Loans Receivable and Related Allowance for Loan Losses - Nonaccrual Loans by Aging Category (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	$ 1,920	$ 3,003
Not Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	604	1,284
30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	0	0
60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	83	75
90 Days and Greater Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	1,233	1,644
Residential first mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	967	856
Residential first mortgages | Not Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	353	366
Residential first mortgages | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	0	0
Residential first mortgages | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	74	75
Residential first mortgages | 90 Days and Greater Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	540	415
Home equity loans and lines of credit
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	542	526
Home equity loans and lines of credit | Not Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	7	8
Home equity loans and lines of credit | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	0	0
Home equity loans and lines of credit | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	9	0
Home equity loans and lines of credit | 90 Days and Greater Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	526	518
Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	309	964
Commercial real estate | Not Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	205	341
Commercial real estate | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	0	0
Commercial real estate | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	0	0
Commercial real estate | 90 Days and Greater Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	104	623
Commercial business
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	39	584
Commercial business | Not Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	39	569
Commercial business | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	0	0
Commercial business | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	0	0
Commercial business | 90 Days and Greater Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	0	15
Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	63	73
Consumer | Not Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	0	0
Consumer | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	0	0
Consumer | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	0	0
Consumer | 90 Days and Greater Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	$ 63	$ 73