Loans and Allowance - Allowance for credit losses (Details)	3 Months Ended		12 Months Ended
	Mar. 31, 2020 USD ($) borrower	Mar. 31, 2019 USD ($) borrower	Dec. 31, 2019 USD ($)
Loans and Allowance
Average loans	$ 281,335,000	$ 299,506,000
Net charge-offs to average loans (annualized)	0.10%	0.15%
Number of borrowers | borrower	14	19
Loans charged off	$ 125,000	$ 205,000	$ 616,000
Outstanding commitments	38,000,000	33,000,000
Unfunded commitments
Beginning balance	37,000	35,000	35,000
Reduction of unfunded reserve		(9,000)
Provisions charged to operations	13,000
Ending balance	$ 50,000	$ 26,000	$ 37,000