Note 5 - Loans (Details Textual) - USD ($)	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Servicing Asset, Total	$ 300,500,000
Impaired Financing Receivable, Recorded Investment, Total	106,886,000	$ 117,353,000
Impaired Financing Receivable, Average Recorded Investment, Total	122,596,000	127,067,000	$ 131,019,000
Impaired Financing Receivable, Interest Income, Accrual Method, Total	$ 3,166,000	$ 3,302,000	3,462,000
Percentage Of Charge Off To Contractual Balances For Impaired Loans	9.30%	7.20%
Allowance for Credit Losses, Change in Method of Calculating Impairment	$ 1,518,000	$ 1,556,000	1,780,000
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	0
Loans and Leases Receivable, Impaired, Commitment to Lend	$ 0
Minimum [Member]
Period Loan Is In Payment Default	60 days
Maximum [Member]
Period Loan Is In Payment Default	90 days
Nonaccrual Loans [Member]
Impaired Financing Receivable, Recorded Investment, Total	$ 41,800,000	48,800,000
Accruing Troubled Debt Restructuring [Member]
Impaired Financing Receivable, Recorded Investment, Total	65,100,000	68,600,000
Financing Receivable, Modifications, Recorded Investment	65,100,000	68,600,000
Allowance for Credit Losses, Change in Method of Calculating Impairment	1,500,000	1,900,000
Non-accruing Troubled Debt Restructuring [Member]
Financing Receivable, Modifications, Recorded Investment	24,200,000	33,400,000
Allowance for Credit Losses, Change in Method of Calculating Impairment	826,000	83,000
Residential Portfolio Segment [Member]
Servicing Asset, Total	103,200,000
Repossessed Assets, Total	862,000	3,500,000
Commercial Real Estate Portfolio Segment [Member]
Servicing Asset, Total	50,800,000
Impaired Financing Receivable, Average Recorded Investment, Total	57,596,000	58,635,000	81,905,000
Impaired Financing Receivable, Interest Income, Accrual Method, Total	2,125,000	1,618,000	2,214,000
Allowance for Credit Losses, Change in Method of Calculating Impairment	111,000	1,496,000	34,000
Commercial Construction Loans [Member]
Servicing Asset, Total	105,900,000
Commercial Portfolio Segment [Member]
Servicing Asset, Total	40,600,000
Impaired Financing Receivable, Average Recorded Investment, Total	44,486,000	26,957,000	21,199,000
Impaired Financing Receivable, Interest Income, Accrual Method, Total	685,000	1,303,000	767,000
Allowance for Credit Losses, Change in Method of Calculating Impairment	1,384,000	7,000	$ 1,746,000
Real Estate Loan [Member]
Federal Home Loan Bank, Advances, General Debt Obligations, Disclosures, Collateral Pledged	9,700,000,000	8,400,000,000
Commercial Loans [Member]
Loans Pledged with Federal Reserve Bank	$ 21,200,000	$ 36,100,000

Amount of the collateral pledged in support of loans with Federal Reserve Bank's Discount Window.

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Amount of allowance for credit losses related to receivables which had been measured under a general allowance for credit losses methodology that are now identified as troubled debt restructurings.

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Amount of the collateral pledged in support of federal home loan bank advances outstanding.

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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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Amount of investment related to financing receivables modified by troubled debt restructurings within the previous 12 months, for which there was a payment default.

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Carrying amount as of the balance sheet date of all assets obtained in full or partial satisfaction of a debt arrangement through foreclosure proceedings or defeasance; includes real and personal property; equity interests in corporations, partnerships, and joint ventures; and beneficial interests in trusts.

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Average 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 interest income recognized that the financing receivables (with related allowance for credit losses and without a related allowance for credit losses) were impaired.

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Reflects the unfunded portion of contractual agreements to lend funds to borrowers for loans whose terms have been modified by troubled debt restructuring.

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Aggregate amount of servicing assets that are subsequently measured at fair value and servicing assets that are subsequently measured using the amortization method.

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