Note 11 - Fair Value Measurements - Discounted Cash Flow Assumptions (Details)	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Minimum [Member]
Time-to-liquidity (Year)	2 years	2 years
Discount rate	4.60%	4.90%
Maximum [Member]
Time-to-liquidity (Year)	3 years	3 years
Discount rate	9.90%	10.10%