Note 5 - Loans (Details Textual) - USD ($)	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Servicing Asset	$ 384,300,000
Impaired Financing Receivable, Recorded Investment	117,353,000	$ 115,074,000
Impaired Financing Receivable, Average Recorded Investment	127,067,000	131,019,000	$ 162,945,000
Impaired Financing Receivable, Interest Income, Accrual Method	$ 3,302,000	$ 3,462,000	3,997,000
Percentage Of Charge Off To Contractual Balances For Impaired Loans	7.20%	8.40%
Allowance for Credit Losses, Change in Method of Calculating Impairment	$ 1,556,000	$ 1,780,000	752,000
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	582,000
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	$ 48,800,000	49,700,000
Accruing Troubled Debt Restructuring [Member]
Impaired Financing Receivable, Recorded Investment	68,600,000	65,400,000
Financing Receivable, Modifications, Recorded Investment	68,600,000	65,400,000
Allowance for Credit Losses, Change in Method of Calculating Impairment	1,900,000	1,300,000
Non-accruing Troubled Debt Restructuring [Member]
Financing Receivable, Modifications, Recorded Investment	33,400,000	29,700,000
Allowance for Credit Losses, Change in Method of Calculating Impairment	83,000	1,100,000
Residential Portfolio Segment [Member]
Servicing Asset	116,900,000
Repossessed Assets	3,500,000	3,600,000
Commercial Real Estate Portfolio Segment [Member]
Servicing Asset	87,700,000
Impaired Financing Receivable, Average Recorded Investment	58,635,000	81,905,000	100,118,000
Impaired Financing Receivable, Interest Income, Accrual Method	1,618,000	2,214,000	2,708,000
Allowance for Credit Losses, Change in Method of Calculating Impairment	1,496,000	34,000	708,000
Commercial Construction Loans [Member]
Servicing Asset	138,300,000
Commercial Portfolio Segment [Member]
Servicing Asset	41,400,000
Impaired Financing Receivable, Average Recorded Investment	26,957,000	21,199,000	23,960,000
Impaired Financing Receivable, Interest Income, Accrual Method	1,303,000	767,000	546,000
Allowance for Credit Losses, Change in Method of Calculating Impairment	7,000	1,746,000	$ 2,000
Real Estate Loan [Member]
Federal Home Loan Bank, Advances, General Debt Obligations, Disclosures, Collateral Pledged	8,400,000,000	7,800,000,000
Commercial Loans [Member]
Loans Pledged with Federal Reserve Bank	$ 36,100,000	$ 30,000,000

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

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Percentage of charge-off to contractual balances for impaired loans.

+ References

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Period Loan Is In Payment Default

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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.

+ References

No definition available.

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- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6479118&loc=d3e64650-112822

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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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-Publisher FASB
-Name Accounting Standards Codification
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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.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
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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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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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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-Publisher FASB
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