Note 12 - Derivative Financial Instruments (Details Textual) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Junior Subordinated Notes, Total	$ 43,910		$ 43,910		$ 41,849
Derivative Asset, Notional Amount	896,752		896,752		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	400	$ 100	1,300	$ 200
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	318,900		318,900		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	337,300		337,300		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