Note 4 - Loans (Details Textual) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2019 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2018 USD ($)
Unamortized Loan Commitment and Origination Fees and Unamortized Discounts or Premiums, Total	$ 2,200		$ 2,500
Loans and Leases Receivable, Impaired, Interest Lost on Nonaccrual Loans	158	$ 43
Impaired Financing Receivable, Recorded Investment, Total	$ 21,215		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	0
Financing Receivable, Nonaccrual	$ 14,535		4,146
Financing Receivable, Troubled Debt Restructuring	$ 9,400		$ 9,600
Financing Receivable, Number of Contracts Qualified as Troubled Debt Restructuring	105
Troubled Debt Restructurings Percentage of Gross Portfolio Loans	0.91%		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	$ 213
Loans and Leases Receivable, Allowance, Ending Balance	$ 12,242		$ 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	$ 220,700		$ 235,800
Reserve for Unfunded Commitments Included in Other Liabilities	$ 595		$ 695
Percentage of Loan Portfolio Secured by Real Estate	82.00%
Percentage of Unallocated Allowance Amount out of Allowance for Loan and Lease Losses	4.00%		4.00%
Maximum Loan to Value, Percentage	80.00%
Commercial Portfolio Segment [Member]
Impaired Financing Receivable, Recorded Investment, Total	$ 2,205		$ 2,183
Financing Receivable, Nonaccrual	$ 1,018		$ 959
Commercial Portfolio Segment [Member] | Line of Credit [Member]
Financing Receivable, Modifications, Number of Contracts	1		1
Financing Receivable, Nonaccrual	$ 41		$ 313
Performing Financial Instruments [Member]
Impaired Financing Receivable, Recorded Investment, Total	$ 6,700		6,900
Financing Receivable, Number of Contracts Qualified as Troubled Debt Restructuring	104
Merchants Holding Company [Member]
Accretion (Amortization) of Discounts and Premiums, Acquired Loans	$ 48
Federal Home Loan Bank of San Francisco [Member]
Loans Pledged as Collateral	$ 480,000		$ 490,200