Loans Receivable and Allowance for Loan Losses, Contract Amounts for Off-Balance Sheet Instruments (Details) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2017 USD ($) Loan	Sep. 30, 2016 Loan	Dec. 31, 2016 USD ($) Commitment
Standby Letters of Credit [Member]
Financial instruments whose contract amount represents credit risk [Abstract]
Letters of credit expiry period	12 months
Off-balance sheet credit risk	$ 3,854		$ 4,022
Current liability for guarantees	79		94
Home Equity Lines of Credit [Member]
Financial instruments whose contract amount represents credit risk [Abstract]
Off-balance sheet credit risk	$ 12,425		7,736
Loan expiry period	10 years
Unadvanced Construction Commitments [Member]
Financial instruments whose contract amount represents credit risk [Abstract]
Off-balance sheet credit risk	$ 72,045		15,728
Mortgage Loan Commitments [Member]
Financial instruments whose contract amount represents credit risk [Abstract]
Off-balance sheet credit risk	0		$ 574
Number of mortgage loan commitments at fixed interest rate | Commitment			2
Fixed rate loan commitments	0		$ 574
Fixed interest rate			4.25%
Lines of Credit [Member]
Financial instruments whose contract amount represents credit risk [Abstract]
Off-balance sheet credit risk	13,092		$ 34,125
Loans Sold and Serviced with Limited Repurchase Provisions [Member]
Financial instruments whose contract amount represents credit risk [Abstract]
Off-balance sheet credit risk	19,979		70,773
Mortgage loan, held in reserve	$ 59		$ 48
Number of repurchased loans | Loan	0	0
Loans Sold and Serviced with Limited Repurchase Provisions [Member] | Minimum [Member]
Financial instruments whose contract amount represents credit risk [Abstract]
Period of delinquency under repurchase agreement	120 days
Loans Sold and Serviced with Limited Repurchase Provisions [Member] | Maximum [Member]
Financial instruments whose contract amount represents credit risk [Abstract]
Period of delinquency under repurchase agreement	180 days