Note 13 - Equity-based Compensation - Weighted-average Assumptions Used in Determining the Value of Options Granted to Employees and Directors (Details) - Employees and Directors [Member] - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Expected price volatility	112.41%	89.30%	87.78%
Expected term (Year)	6 years 51 days	5 years 357 days	6 years 328 days
Risk-free interest rate	1.99%	2.80%	2.12%
Dividend yield	0.00%	0.00%	0.00%
Weighted-average fair value of options granted during the period (in dollars per share)	$ 0.31	$ 1.51	$ 2.34