Note 4 - Fair Value Measurement - Discounted Cash Flow Assumptions (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Minimum [Member]
Time-to-liquidity (Year)	2 years	2 years
Discount rate	4.90%	4.50%
Maximum [Member]
Time-to-liquidity (Year)	3 years	3 years
Discount rate	10.10%	9.60%