Note 11 - Derivative Financial Instruments (Details Textual) - USD ($) $ in Thousands		3 Months Ended
Mar. 31, 2018	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Junior Subordinated Notes, Total	$ 38,692	$ 38,692		$ 36,986
Derivative Asset, Notional Amount	741,113	741,113		739,726
Short-term Debt, Total	441,500	441,500		441,500
Derivative, Net Hedge Ineffectiveness Gain (Loss)	0		$ 0
Cash Flow Hedging [Member] \| Interest Expense [Member]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net, Total		300
Not Designated as Hedging Instrument [Member]
Derivative Asset, Notional Amount	36,300	36,300		36,300
Designated as Hedging Instrument [Member]
Derivative Asset, Notional Amount	263,300	263,300		261,900
Designated as Hedging Instrument [Member] \| Cash Flow Hedging [Member]
Derivative Asset, Notional Amount	441,500	441,500		441,500
Interest Rate Swap [Member]
Derivative Asset, Notional Amount	281,600	281,600		280,200
Interest Rate Swap [Member] \| Not Designated as Hedging Instrument [Member] \| Cash Flow Hedging [Member]
Derivative Asset, Notional Amount	36,321	36,321		36,321
Floating Rate Junior Subordinated Debentures [Member]
Derivative, Amount of Hedged Item	18,000	18,000		18,000
Junior Subordinated Notes, Total	$ 61,900	$ 61,900		$ 61,900

Amount of hedged item in hedging relationship. Excludes hedged asset or liability.

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Nominal or face amount used to calculate payments on the derivative asset.

+ References

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-Publisher FASB
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The effective portion of net gain (loss) reclassified from accumulated other comprehensive income into income on derivative instruments designated and qualifying as hedging instruments.

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Amount of gain (loss) from the ineffectiveness of the hedge.

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Including the current and noncurrent portions, carrying value as of the balance sheet date of long-term debt (with maturities initially due after one year or beyond the operating cycle if longer) identified as Junior Subordinated Notes, which have a lower priority than senior instruments.

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