Loans Receivable and Related Allowance for Loan Losses - Summary of Loans (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans, gross	$ 583,361	$ 520,980
Less allowance for loan losses	6,127	5,545	$ 5,205
Total loans, net	577,234	515,435
Residential first mortgages
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans, gross	221,823	198,167
Less allowance for loan losses	2,090	1,846	1,429
Home equity loans and lines of credit
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans, gross	99,940	91,359
Less allowance for loan losses	646	633	586
Commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans, gross	193,068	166,994
Less allowance for loan losses	2,753	2,314	2,185
Commercial business
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans, gross	58,941	57,788
Less allowance for loan losses	585	700	960
Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans, gross	9,589	6,672
Less allowance for loan losses	53	52	$ 45
Mortgage loans on real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans, gross	514,831	456,520
Mortgage loans on real estate \| Residential first mortgages
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans, gross	221,823	198,167
Mortgage loans on real estate \| Home equity loans and lines of credit
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans, gross	99,940	91,359
Mortgage loans on real estate \| Commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans, gross	193,068	166,994
Other loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans, gross	68,530	64,460
Other loans \| Commercial business
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans, gross	58,941	57,788
Other loans \| Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans, gross	$ 9,589	$ 6,672

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Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

+ References

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Amount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements.

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Amount after allowance and deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements and loans held for sale.

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