Note 4 - Loans (Details Textual) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2018 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)
Unamortized Loan Commitment and Origination Fees and Unamortized Discounts or Premiums, Total	$ 2,800		$ 2,800
Loans and Leases Receivable, Impaired, Interest Lost on Nonaccrual Loans	43	$ 104
Impaired Financing Receivable, Recorded Investment, Total	$ 11,462		13,147
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, Recorded Investment, Nonaccrual Status	$ 4,216		5,799
Financing Receivable, Modifications, Recorded Investment	$ 10,500		$ 10,900
Financing Receivable, Number of Contracts Qualified as Troubled Debt Restructuring	113
Troubled Debt Restructurings Percentage of Gross Portfolio Loans	1.16%		1.24%
Financing Receivable, Modifications, Subsequent Default, Number of Contracts	0	0
Doubtful Grade Remaining Outstanding Period, Minimum	180 days
Mortgage Loans in Process of Foreclosure, Amount	$ 308
Loans and Leases Receivable, Allowance, Ending Balance	$ 12,295		$ 11,925
Percentage of Allowance for Loan and Lease Losses out of Net Loans	1.37%		1.36%
Fair Value Disclosure, Off-balance Sheet Risks, Amount, Asset	$ 232,900		$ 227,700
Reserve for Unfunded Commitments Included in Other Liabilities	$ 695		$ 695
Percentage of Loan Portfolio Secured by Real Estate	80.00%
Percentage of Unallocated Allowance Amount out of Allowance for Loan and Lease Losses	4.00%		3.00%
Maximum Loan to Value, Percentage	80.00%
Commercial Portfolio Segment [Member]
Impaired Financing Receivable, Recorded Investment, Total	$ 2,625		$ 3,154
Financing Receivable, Recorded Investment, Nonaccrual Status	$ 1,109		$ 1,603
Commercial Portfolio Segment [Member] \| Line of Credit [Member]
Financing Receivable, Modifications, Number of Contracts	1		1
Financing Receivable, Recorded Investment, Nonaccrual Status	$ 295		$ 33
Performing Financial Instruments [Member]
Impaired Financing Receivable, Recorded Investment, Total	$ 7,200		7,300
Financing Receivable, Number of Contracts Qualified as Troubled Debt Restructuring	108
Federal Home Loan Bank of San Francisco [Member]
Loans Pledged as Collateral	$ 445,300		$ 420,000

Period that a loan classified as Doubtful will remain outstanding.

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Number of financing receivables that qualified as troubled debt restructurings.

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The maximum loan to value percentage.

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Percentage of the allowance for loan and lease losses as a percentage of total gross loans.

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The percentage of collateral coverage to loan balance, to consider restructured loan to performing and accrual status.

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The percentage of the gross loan portfolio that is secured by real estate.

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The percentage of unallocated allowance amount out of allowance for loan and lease losses.

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Amount of the reserve for unfunded commitments.

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Percentage of gross portfolio loans that are classified as loans modified under a troubled debt restructuring.

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The fair value of financial assets, which are not recognized in the financial statements (off-balance sheet) because they fail to meet some other criterion for recognition.

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Number of financing receivables that have been modified by troubled debt restructurings.

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The amount of the outstanding recorded investment related to financing receivables that have been modified by troubled debt restructurings.

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Number of financing receivables that have been modified by troubled debt restructurings within the previous 12 months and for which there was a payment default.

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Recorded investment in financing receivables that are on nonaccrual status as of the balance sheet date.

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Amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

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Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

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Reflects the amount of additional interest income that would have been recorded if impaired or nonperforming loans were instead current, in compliance with their original terms, and outstanding throughout the reporting period or since origination (if held for part of the period).

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Carrying amount as of the balance sheet date of loans that have been pledged as collateral for borrowings. If the secured party has the right by contract or custom to sell or re-pledge the collateral, then the debtor reclassifies that asset and report that asset in its statement of financial position separately from other assets not so encumbered.

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Recorded investment of consumer mortgage loan receivables secured by residential real estate properties for which formal foreclosure proceedings are in process.

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Amount of deferred fees paid by borrowers and unamortized costs incurred to originate loans and leases, unamortized loan commitments and loan syndication fees, and premiums over or discounts from face amounts of loans that are being amortized into income as an adjustment to yield. Excludes amounts for loans and leases covered under loss sharing agreements.

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