Note 10 - Stockholders' Equity - Summary of Warrants Outstanding (Details)	Jun. 30, 2019 $ / shares shares
Warrants outstanding (in shares)	12,832,188
First Set of Warrants Expiring April 2024 [Member]
Warrants outstanding (in shares)	1,646,364
Exercise Price (in dollars per share) | $ / shares	$ 0.10
Second Set of Warrants Expiring April 2024 [Member]
Warrants outstanding (in shares)	10,454,546
Exercise Price (in dollars per share) | $ / shares	$ 1.10
Third Set of Warrants Expiring April 2024 [Member]
Warrants outstanding (in shares)	636,364
Exercise Price (in dollars per share) | $ / shares	$ 1.375
Warrants Expiring March 2024 [Member]
Warrants outstanding (in shares)	84,000
Exercise Price (in dollars per share) | $ / shares	$ 3.125
Warrants Expiring December 2026 [Member]
Warrants outstanding (in shares)	10,914
Exercise Price (in dollars per share) | $ / shares	$ 22.99