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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 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. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=82891408&loc=d3e4428-111522 + Details
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