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, 2020	Dec. 31, 2019	Dec. 31, 2018
Collateralized Debt Obligations [Member]
Balance	$ 0	$ 0	$ 489
Security transferred to Level 3 measurement	0	0	0
Unrealized (losses) gains	0	0	237
Paydowns	0	0	0
Proceeds from sales	0	0	(660)
Realized losses	0	0	(66)
Impairment charges on Level 3	0	0	0
Balance	0	0	0
Corporate Debt Securities [Member]
Balance	2,820	3,069	3,086
Security transferred to Level 3 measurement	0	0	0
Unrealized (losses) gains	(189)	(249)	(17)
Paydowns	0	0	0
Proceeds from sales	0	0	0
Realized losses	0	0	0
Impairment charges on Level 3	0	0	0
Balance	$ 2,631	$ 2,820	$ 3,069