Loans Receivable and Allowance for Loan Losses - Activity in Allowance for Loan Losses (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Activity in allowance for loan losses
Balance, beginning of period	$ 2,918,000	$ 2,659,000	$ 2,712,000	$ 2,642,000
Provision (reversal of provision) for loan losses	1,395,000	(51,000)	1,612,000	(46,000)
Allowance for loan losses on loans receivable after provision (reversal of allowance)	4,313,000	2,608,000	4,324,000	2,596,000
Charge-offs	(68,000)	(9,000)	(80,000)	(16,000)
Recoveries	11,000	17,000	12,000	36,000
Net recoveries (charge-offs)	(57,000)	8,000	(68,000)	20,000
Balance, end of period	4,256,000	2,616,000	4,256,000	2,616,000
Residential Mortgage
Activity in allowance for loan losses
Balance, beginning of period	1,863,000	1,800,000	1,741,000	1,797,000
Provision (reversal of provision) for loan losses	1,157,000	(31,000)	1,279,000	(46,000)
Allowance for loan losses on loans receivable after provision (reversal of allowance)	3,020,000	1,769,000	3,020,000	1,751,000
Recoveries				18,000
Net recoveries (charge-offs)				18,000
Balance, end of period	3,020,000	1,769,000	3,020,000	1,769,000
Construction, Commercial and Other Mortgage Loans
Activity in allowance for loan losses
Balance, beginning of period	452,000	454,000	511,000	443,000
Provision (reversal of provision) for loan losses	7,000	(43,000)	(52,000)	(32,000)
Allowance for loan losses on loans receivable after provision (reversal of allowance)	459,000	411,000	459,000	411,000
Balance, end of period	459,000	411,000	459,000	411,000
Home Equity Loans and Lines of Credit
Activity in allowance for loan losses
Balance, beginning of period	1,000	1,000	1,000	1,000
Provision (reversal of provision) for loan losses	(10,000)		(10,000)
Allowance for loan losses on loans receivable after provision (reversal of allowance)	(9,000)	1,000	(9,000)	1,000
Recoveries	10,000		10,000
Net recoveries (charge-offs)	10,000		10,000
Balance, end of period	1,000	1,000	1,000	1,000
Consumer and other loans
Activity in allowance for loan losses
Balance, beginning of period	172,000	45,000	54,000	47,000
Provision (reversal of provision) for loan losses	92,000	(9,000)	221,000	(5,000)
Allowance for loan losses on loans receivable after provision (reversal of allowance)	264,000	36,000	275,000	42,000
Charge-offs	(68,000)	(9,000)	(80,000)	(16,000)
Recoveries	1,000	17,000	2,000	18,000
Net recoveries (charge-offs)	(67,000)	8,000	(78,000)	2,000
Balance, end of period	197,000	44,000	197,000	44,000
Unallocated
Activity in allowance for loan losses
Balance, beginning of period	430,000	359,000	405,000	354,000
Provision (reversal of provision) for loan losses	149,000	32,000	174,000	37,000
Allowance for loan losses on loans receivable after provision (reversal of allowance)	579,000	391,000	579,000	391,000
Balance, end of period	$ 579,000	$ 391,000	$ 579,000	$ 391,000