Note 4 - Loans (Details Textual) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)
Unamortized Loan Commitment and Origination Fees and Unamortized Discounts or Premiums, Total	$ 1,700		$ 1,700		$ 2,500
Loans and Leases Receivable, Impaired, Interest Lost on Nonaccrual Loans	115	$ 40	484	$ 121
Impaired Financing Receivable, Recorded Investment, Total	$ 17,733		$ 17,733		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		0	1	0
Financing Receivable, Nonaccrual	$ 12,796		$ 12,796		4,146
Financing Receivable, Troubled Debt Restructuring	$ 6,700		$ 6,700		$ 9,600
Financing Receivable, Number of Contracts Qualified as Troubled Debt Restructuring	99		99
Troubled Debt Restructurings Percentage of Gross Portfolio Loans	0.65%		0.65%		1.01%
Financing Receivable, Troubled Debt Restructuring, Subsequent Default, Number of Contracts	0		0
Doubtful Grade Remaining Outstanding Period, Minimum			180 days
Mortgage Loans in Process of Foreclosure, Amount	$ 250		$ 250
Loans and Leases Receivable, Allowance, Ending Balance	$ 12,285		$ 12,285		$ 12,292
Percentage of Allowance for Loan and Lease Losses out of Net Loans	1.19%		1.19%		1.30%
Fair Value Disclosure, Off-balance Sheet Risks, Amount, Asset	$ 269,500		$ 269,500		$ 235,800
Reserve for Unfunded Commitments Included in Other Liabilities	$ 695		$ 695		$ 695
Percentage of Loan Portfolio Secured by Real Estate	81.00%		81.00%
Percentage of Unallocated Allowance Amount out of Allowance for Loan and Lease Losses			5.00%		4.00%
Maximum Loan to Value, Percentage			80.00%
Commercial Portfolio Segment [Member]
Impaired Financing Receivable, Recorded Investment, Total	$ 768		$ 768		$ 2,183
Financing Receivable, Modifications, Number of Contracts			1
Financing Receivable, Nonaccrual	$ 139		$ 139		$ 959
Commercial Portfolio Segment [Member] | Line of Credit [Member]
Financing Receivable, Modifications, Number of Contracts					1
Financing Receivable, Nonaccrual					$ 313
Performing Financial Instruments [Member]
Impaired Financing Receivable, Recorded Investment, Total	$ 4,900		$ 4,900		6,900
Financing Receivable, Number of Contracts Qualified as Troubled Debt Restructuring	97		97
Merchants Holding Company [Member]
Unamortized Loan Commitment and Origination Fees and Unamortized Discounts or Premiums, Total	$ 1,900		$ 1,900
Accretion (Amortization) of Discounts and Premiums, Acquired Loans	193		431
Federal Home Loan Bank of San Francisco [Member]
Loans Pledged as Collateral	$ 527,500		$ 527,500		$ 490,200