Note 12 - Stockholders' Equity - Summary of Warrants Outstanding (Details)	Dec. 31, 2019 $ / shares shares
Warrants outstanding (in shares)	43,370,162
First Set of Warrants Expiring September 2024 [Member]
Warrants outstanding (in shares)	30,068,600
Exercise Price (in dollars per share) | $ / shares	$ 0.30
Second Set of Warrants Expiring September 2024 [Member]
Warrants outstanding (in shares)	2,115,738
Exercise Price (in dollars per share) | $ / shares	$ 0.375
Third Set of Warrants Expiring September 2024 [Member]
Warrants outstanding (in shares)	10,454,546
Exercise Price (in dollars per share) | $ / shares	$ 1.10
First Set of Warrants Expiring April 2024 [Member]
Warrants outstanding (in shares)	636,364
Exercise Price (in dollars per share) | $ / shares	$ 1.375
Second Set of Warrants Expiring April 2024 [Member]
Warrants outstanding (in shares)	84,000
Exercise Price (in dollars per share) | $ / shares	$ 3.125
Warrants Expiring March 2024 [Member]
Warrants outstanding (in shares)	10,914
Exercise Price (in dollars per share) | $ / shares	$ 22.99