Note 12 - Derivative Financial Instruments (Details Textual) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Mar. 31, 2019	Dec. 31, 2018
Junior Subordinated Notes, Total	$ 43,414		$ 43,414			$ 41,849
Derivative Asset, Notional Amount	841,690		841,690			745,619
Short-term Debt, Total	541,500		541,500			441,500
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net, Total	600	$ 300	800	$ 400
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	263,900		263,900			267,800
Designated as Hedging Instrument [Member] | Cash Flow Hedging [Member]
Derivative Asset, Notional Amount	541,500		541,500		$ 441,500
Interest Rate Swap [Member]
Derivative Asset, Notional Amount	282,200		282,200			286,100
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