Note 15 - Fair Value Measurements and Fair Values of Financial Instruments - Assets Measured on a Recurring Basis Using Significant Unobservable Inputs (Details) - Fair Value, Inputs, Level 3 [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Collateralized Debt Obligations [Member]
Balance	$ 1,820	$ 1,883	$ 3,193
Security transferred to Level 3 measurement
Unrealized (losses) gains	1,006	(56)	882
Paydowns			(19)
Proceeds from sales	(1,539)		(1,952)
Realized losses	(798)		(218)
Impairment charges on Level 3		(7)	(3)
Balance	489	1,820	1,883
Corporate Debt Securities [Member]
Balance	2,971	2,834	3,005
Security transferred to Level 3 measurement
Unrealized (losses) gains	115	137	(171)
Paydowns
Proceeds from sales
Realized losses
Impairment charges on Level 3
Balance	$ 3,086	$ 2,971	$ 2,834