Goodwill and Other Intangibles and Mortgage Servicing Rights - Mortgage servicing rights (Details) - Mortgage Servicing Rights - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Mortgage servicing rights ("MSR") asset:
MSR asset at beginning of year	$ 5,919,000	$ 3,749,000
Capitalized MSR	4,038,000	2,876,000
MSR asset acquired	529,000	160,000
Amortization during the period	(1,001,000)	(866,000)
MSR asset at end of period	9,485,000	5,919,000
Valuation Allowance:
Valuation allowance at beginning of year	0	0
Additions	(800,000)	0
Valuation allowance at end of period	(800,000)	0
MSR asset, net	8,685,000	5,919,000
Fair value of MSR asset at end of period	10,332,000	8,420,000
Residential mortgage loans serviced for others	$ 1,204,856,000	$ 847,756,000
Net book value of MSR asset to loans serviced for others	0.72%	0.70%