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Note 1 - Significant Accounting Policies (Details Textual) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2018 USD ($) shares	Mar. 31, 2017 shares	Dec. 31, 2018	Dec. 31, 2017 USD ($)
Number of Unconsolidated Business Trusts Formed to Issue Trust Preferred Securities	5
Interest Income on Commercial and Mortgage Loans Discontinued Period	90 days
Maximum Delinquency Period for Consumer and Credit Card Loans to be Charged Off	120 days
Loans Receivable Held-for-sale, Net, Not Part of Disposal Group, Mortgage | $	$ 1.9			$ 2.6
Servicing Asset, Total | $	$ 611.0
Adjustments for New Accounting Principle, Early Adoption [Member]
Reclassification from AOCI to Retained Earnings, Current Period | $				$ 0.9
Scenario, Forecast [Member]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent			21.00%
Core Deposits [Member]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	10 years
Restricted Stock [Member]
Incremental Common Shares Attributable to Participating Nonvested Shares with Non-forfeitable Dividend Rights | shares	236,000	225,000
Employee Stock Option [Member]
Incremental Common Shares Attributable to Participating Nonvested Shares with Non-forfeitable Dividend Rights | shares	17,000	34,000
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount | shares	7,000	7,000

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- Definition

Number of days past due when interest income on commercial and mortgage loans is discontinued unless the loans are well-secured and in process of collection.

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Maximum number of days delinquent for consumer and credit card loans to be charged off.

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The number of unconsolidated business trusts formed to issue trust preferred securities.

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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This element represents nonvested share-based payment awards that contain non-forfeitable rights to dividends or dividend equivalents (whether paid or unpaid). Basic and dilutive earnings per share are generally disclosed for such shares using the two-class method.

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Amount, after allowance for bad debt, of mortgage loan receivables held-for-sale that are not part of a disposal group. Excludes loans and leases covered under loss sharing agreements and loans classified as debt securities.

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