Note 5 - Loans (Details Textual) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2019 USD ($)
Unamortized Loan Commitment and Origination Fees and Unamortized Discounts or Premiums, Total	$ 1,500	$ 2,500
Loans and Leases Receivable, Impaired, Interest Lost on Nonaccrual Loans	254	166
Financing Receivable, Nonaccrual	5,616	4,146
Impaired Financing Receivable, Recorded Investment, Total	$ 10,399	11,012
Percentage of Collateral Coverage to Loan Balance to Consider Restructured Loan to Performing and Accrual Status	100.00%
Financing Receivable, Modifications, Number of Contracts	2
Financing Receivable, Troubled Debt Restructuring	$ 6,500	$ 9,600
Financing Receivable, Number of Contracts Qualified as Troubled Debt Restructuring	98
Troubled Debt Restructurings Percentage of Gross Portfolio Loans	0.63%	1.01%
Financing Receivable, Troubled Debt Restructuring, Subsequent Default, Number of Contracts	0
Doubtful Grade Remaining Outstanding Period, Minimum	180 days
Mortgage Loans in Process of Foreclosure, Amount	$ 100
Loans and Leases Receivable, Allowance, Ending Balance	$ 12,231	$ 12,292
Percentage of Allowance for Loan and Lease Losses out of Net Loans	1.18%	1.30%
Fair Value Disclosure, Off-balance Sheet Risks, Amount, Asset	$ 275,100	$ 235,800
Reserve for Unfunded Commitments Included in Other Liabilities	$ 695	$ 695	$ 695
Percentage of Loan Portfolio Secured by Real Estate	83.00%
Percentage of Unallocated Allowance Amount out of Allowance for Loan and Lease Losses	3.00%	4.00%
Maximum Loan to Value, Percentage	80.00%
Performing Financial Instruments [Member]
Impaired Financing Receivable, Recorded Investment, Total	$ 4,800	$ 6,900
Financing Receivable, Number of Contracts Qualified as Troubled Debt Restructuring	94
Commercial Portfolio Segment [Member]
Financing Receivable, Nonaccrual	$ 61	959
Impaired Financing Receivable, Recorded Investment, Total	$ 656	2,183
Financing Receivable, Modifications, Number of Contracts	1
Commercial Portfolio Segment [Member] | Real Estate Loan [Member]
Financing Receivable, Nonaccrual	$ 9,900
Commercial Portfolio Segment [Member] | Line of Credit [Member]
Financing Receivable, Nonaccrual		$ 313
Financing Receivable, Modifications, Number of Contracts		1
Consumer Portfolio Segment [Member]
Financing Receivable, Nonaccrual	40	$ 23
Impaired Financing Receivable, Recorded Investment, Total	$ 40	23
Financing Receivable, Modifications, Number of Contracts	1
Financing Receivable, Troubled Debt Restructuring	$ 20
Merchants Holding Company [Member]
Unamortized Loan Commitment and Origination Fees and Unamortized Discounts or Premiums, Total	1,700
Accretion (Amortization) of Discounts and Premiums, Acquired Loans	620
Federal Home Loan Bank of San Francisco [Member]
Loans Pledged as Collateral	$ 542,100	$ 490,200