Note 4 - Fair Value Measurements - Discounted Cash Flow Assumptions (Details)		12 Months Ended
		Dec. 31, 2020		Dec. 31, 2019
Minimum [Member]
Time-to-liquidity (Year)		2 years	[1]	2 years
Discount rate		3.50%	[1]	4.00%
Maximum [Member]
Time-to-liquidity (Year)		3 years	[1]	3 years
Discount rate		7.90%	[1]	8.30%
Weighted Average [Member]
Time-to-liquidity (Year)	[1]	2 years 6 months
Discount rate	[1]	(5.60%)

[1] The parenthetical value represents the weighted average assumption, which was calculated based on the relative fair value of the securities.