Note 10 - Fair Value Measurements - Discounted Cash Flow Assumptions (Details)		3 Months Ended	12 Months Ended
		Mar. 31, 2020	Dec. 31, 2019
Minimum [Member]
Time-to-liquidity (Year)		2 years	2 years
Discount rate		3.10%	4.00%
Maximum [Member]
Time-to-liquidity (Year)		3 years	3 years
Discount rate		7.30%	8.30%
Weighted Average [Member]
Time-to-liquidity (Year)	[1]	2 years 6 months
Discount rate	[1]	(5.00%)

[1] The parenthetical information represents the weighted-average values, which were calculated based on the relative fair value of the securities.