Note 10 - Derivatives and Risk Management Activities - Derivative Instrument Gain (Loss) Recorded in Statement of Income (Details) - Mortgage Banking Income [Member] - Not Designated as Hedging Instrument [Member] - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Best Efforts Forward Loan sales Commitments [Member] | Liability Derivatives [Member]
Derivative Gain (Loss), Net	$ 17	$ 107	$ (118)	$ (38)
Mandatory Forward Loan Sales Commitments [Member] | Liability Derivatives [Member]
Derivative Gain (Loss), Net	(152)	(23)	(105)	(110)
Interest Rate Lock Commitments [Member] | Liability Derivatives [Member]
Derivative Gain (Loss), Net	(1)	6	(1)	54
Asset Derivatives [Member] | Best Efforts Forward Loan sales Commitments [Member]
Derivative Gain (Loss), Net	(5)	18	(5)	(82)
Asset Derivatives [Member] | Mandatory Forward Loan Sales Commitments [Member]
Derivative Gain (Loss), Net	3	(4)	(13)	(225)
Asset Derivatives [Member] | Interest Rate Lock Commitments [Member]
Derivative Gain (Loss), Net	$ 80	$ (71)	$ 351	$ 321