Loans Receivable and Related Allowance for Loan Losses - Summary of Loans (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	$ 590,177	$ 583,361
Less allowance for loan losses	5,935	6,127	$ 5,688	$ 5,545
Total loans, net	584,242	577,234
Residential first mortgages
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	224,690	221,823
Less allowance for loan losses	1,919	2,090	1,956	1,846
Home equity loans and lines of credit
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	100,241	99,940
Less allowance for loan losses	651	646	648	633
Commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	196,788	193,068
Less allowance for loan losses	2,751	2,753	2,449	2,314
Commercial business
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	59,200	58,941
Less allowance for loan losses	560	585	583	700
Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	9,258	9,589
Less allowance for loan losses	54	53	$ 52	$ 52
Mortgage loans on real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	521,719	514,831
Mortgage loans on real estate | Residential first mortgages
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	224,690	221,823
Mortgage loans on real estate | Home equity loans and lines of credit
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	100,241	99,940
Mortgage loans on real estate | Commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	196,788	193,068
Other loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	68,458	68,530
Other loans | Commercial business
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	59,200	58,941
Other loans | Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	$ 9,258	$ 9,589