Note 15 - Financial Derivatives (Details Textual) - USD ($)		3 Months Ended		9 Months Ended
	May 31, 2014	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Junior Subordinated Notes, Total	$ 119,100,000
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax		$ 1,666,000	$ 157,000	$ 4,595,000	$ (94,000)
Cash [Member]
Collateral Already Posted, Aggregate Fair Value		0		0		$ 4,500,000
Interest Rate Swap [Member] | Cash Flow Hedging [Member] | Designated as Hedging Instrument [Member]
Derivative Outstanding, Notional Amount	$ 119,100,000	$ 119,100,000		$ 119,100,000
Derivative Original Maturity	10 years
Derivative, Average Fixed Interest Rate	2.61%
Derivative, Average Variable Interest Rate		2.35%		2.35%
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax				$ 1,900,000	2,300,000
Net Accrued on Interest Rate Swaps		$ 83,000	407,000	480,000	1,300,000
Interest Rate Swap [Member] | Fair Value Hedging [Member] | Designated as Hedging Instrument [Member]
Derivative Outstanding, Notional Amount		$ 637,700,000	510,600,000	$ 637,700,000	510,600,000
Derivative, Average Fixed Interest Rate		4.71%		4.71%
Derivative, Average Variable Interest Rate		4.78%		4.78%
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax				$ 15,700,000	1,900,000
Net Accrued on Interest Rate Swaps		$ 96,000	$ 514,000	$ 132,000	$ 1,900,000
Interest Rate Swap [Member] | Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | London Interbank Offered Rate (LIBOR) [Member]
Derivative, Average Basis Spread on Variable Rate		2.66%		2.66%
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		$ 1,600,000		$ 1,600,000		1,000,000
Open Option Contracts Fair Value		4,000		4,000		9,000
Sum Of Spot And Forward Contract Notional Amount		117,600,000		117,600,000		32,100,000
Negative Fair Value		1,600,000		1,600,000		453,000
Positive Fair Value [Member]
Sum Of Spot And Forward Contract Notional Amount		53,400,000		53,400,000		108,500,000
Positive Fair Value		$ 400,000		$ 400,000		$ 1,800,000