Note 10 - Stockholders' Equity - Summary of Warrants Outstanding (Details)	Jun. 30, 2020 $ / shares shares
Warrants outstanding (in shares)	1,942,654
First Set of Warrants Expiring September 2024 [Member]
Warrants outstanding (in shares)	171,667
Exercise Price (in dollars per share) | $ / shares	$ 0.30
Second Set of Warrants Expiring September 2024 [Member]
Warrants outstanding (in shares)	241,169
Exercise Price (in dollars per share) | $ / shares	$ 0.375
First Set of Warrants Expiring April 2024 [Member]
Warrants outstanding (in shares)	225,966
Exercise Price (in dollars per share) | $ / shares	$ 1.10
Second Set of Warrants Expiring April 2024 [Member]
Warrants outstanding (in shares)	163,068
Exercise Price (in dollars per share) | $ / shares	$ 1.375
Warrants Expiring March 2025 [Member]
Warrants outstanding (in shares)	766,584
Exercise Price (in dollars per share) | $ / shares	$ 2.50
Warrants Expiring February 2025 [Member]
Warrants outstanding (in shares)	280,000
Exercise Price (in dollars per share) | $ / shares	$ 3.125
Warrants Expiring March 2024 [Member]
Warrants outstanding (in shares)	83,286
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