Note 1 - Significant Accounting Policies (Details Textual) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2018 USD ($) shares	Jun. 30, 2017 shares	Jun. 30, 2018 USD ($) shares	Jun. 30, 2017 shares	Dec. 31, 2018	Dec. 31, 2017 USD ($)
Number of Unconsolidated Business Trusts Formed to Issue Trust Preferred Securities	5		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 | $	$ 3.1		$ 3.1			$ 2.6
Servicing Asset, Total | $	$ 610.0		$ 610.0
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	234,000	220,000	234,000	220,000
Employee Stock Option [Member]
Incremental Common Shares Attributable to Participating Nonvested Shares with Non-forfeitable Dividend Rights | shares	17,000	34,000	17,000	34,000
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount | shares	7,000	7,000	7,000	7,000