Note 14 - Financial Derivatives (Details Textual)		12 Months Ended
	May 31, 2014 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Sep. 30, 2017 USD ($)
Junior Subordinated Notes	$ 119,100,000	$ 119,136,000
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax		719,000	$ 825,000	$ (598,000)
Cash [Member]
Collateral Already Posted, Aggregate Fair Value		4,500,000	6,900,000
Interest Rate Swap [Member] | Cash Flow Hedging [Member] | Designated as Hedging Instrument [Member]
Derivative Asset, Number of Instruments Held	5
Derivative Outstanding, Notional Amount	$ 119,100,000				$ 119,100,000
Derivative Original Maturity	10 years
Derivative, Average Fixed Interest Rate	2.61%
Derivative, Average Variable Interest Rate	1.60%
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax		(1,500,000)	(2,200,000)
Net Accrued on Interest Rate Swaps		1,700,000	2,300,000
Interest Rate Swap [Member] | Fair Value Hedging [Member] | Designated as Hedging Instrument [Member]
Derivative Outstanding, Notional Amount		$ 540,400,000	361,500,000
Derivative, Average Fixed Interest Rate		4.60%
Derivative, Average Variable Interest Rate		4.30%
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax		$ 5,000,000		$ 938,000
Net Accrued on Interest Rate Swaps		2,400,000	3,600,000
Derivative, Notional Amount at Origination		$ 540,400,000
Derivative, Average Basis Spread on Variable Rate		2.89%
Interest Rate Swap [Member] | Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | Minimum [Member]
Derivative Original Maturity		2 years
Interest Rate Swap [Member] | Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | Maximum [Member]
Derivative Original Maturity		10 years
Negative Fair Value [Member]
Notional Amount Of Option Contract		$ 1,000,000	12,100,000
Open Option Contracts Fair Value		9,000	121,000
Sum Of Spot And Forward Contract Notional Amount		32,100,000	89,500,000
Negative Fair Value		453,000	3,100,000
Positive Fair Value [Member]
Sum Of Spot And Forward Contract Notional Amount		108,500,000	82,400,000
Positive Fair Value		$ 1,800,000	$ 1,300,000