Commitments and Contingencies (Details)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) item	Jun. 30, 2017 USD ($)	Dec. 31, 2017 USD ($) item
Financial instruments whose contract amount represents credit risk [Abstract]
Deposits	$ 621,615,000		$ 621,615,000		$ 602,228,000
Loan balances	678,655,000		678,655,000		660,096,000
Interest income	6,927,000	$ 6,007,000	13,911,000	$ 11,593,000
Noninterest Income	2,192,000	1,005,000	4,061,000	2,363,000
Standby Letters of Credit [Member]
Financial instruments whose contract amount represents credit risk [Abstract]
Off-balance sheet credit risk	9,171,000		$ 9,171,000		3,480,000
Letters of credit expiry period			12 months
Letters of credit renewal period			1 year
Current liability for guarantees	50,000		$ 50,000		42,000
Home Equity Lines of Credit [Member]
Financial instruments whose contract amount represents credit risk [Abstract]
Off-balance sheet credit risk	16,959,000		$ 16,959,000		13,321,000
Loan expiry period			10 years
Unadvanced Construction Commitments [Member]
Financial instruments whose contract amount represents credit risk [Abstract]
Off-balance sheet credit risk	49,120,000		$ 49,120,000		74,720,000
Mortgage Loan Commitments [Member]
Financial instruments whose contract amount represents credit risk [Abstract]
Off-balance sheet credit risk	1,067,000		$ 1,067,000		$ 595,000
Number of mortgage loan commitments at fixed interest rate | item			4		2
Fixed rate loan commitments	1,100,000		$ 1,100,000		$ 595,000
Lines of Credit [Member]
Financial instruments whose contract amount represents credit risk [Abstract]
Off-balance sheet credit risk	23,368,000		23,368,000		16,612,000
Loans Sold and Serviced with Limited Repurchase Provisions [Member]
Financial instruments whose contract amount represents credit risk [Abstract]
Off-balance sheet credit risk	34,475,000		34,475,000		21,409,000
Mortgage loan, held in reserve	74,000		74,000		63,000
Repurchases of loans previously sold			$ 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
Business activities with medical-use cannabis customers [Member] | Cannabis Customers
Financial instruments whose contract amount represents credit risk [Abstract]
Deposits	27,800,000		$ 27,800,000		19,200,000
Loan balances	$ 15,300,000		$ 15,300,000		$ 11,900,000
Percentage of deposits in total deposits	4.50%		4.50%		3.20%
Percentage of loans in total loans	2.20%		2.20%		1.80%
Interest income	$ 134,000	$ 0	$ 310,000	0
Noninterest Income	315,000		545,000
Volume of deposits accepted	$ 11,400,000		$ 29,300,000	$ 0