Note 11 - Fair Value Measurements - Discounted Cash Flow Assumptions (Details)	6 Months Ended	12 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Minimum [Member]
Time-to-liquidity (Year)	2 years	2 years
Discount rate	4.10%	4.90%
Maximum [Member]
Time-to-liquidity (Year)	3 years	3 years
Discount rate	9.40%	10.10%