Note 12 - Stockholders' Equity - Outstanding Warrants (Details) - $ / shares	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Sep. 30, 2019
Outstanding warrants (in shares)			544,000
Outstanding warrants, weighted-average exercise price (in dollars per share)			$ 1.81
Warrants granted (in shares)			8,438,000
Warrants granted, weighted average exercise price (in dollars per share)			$ 1.11
Warrants exercised (in shares)	(102,602)	(158,400)	(394,000)
Warrants exercised, weighted average exercise price (in dollars per share)			$ 0.21
Warrants expired (in shares)
Warrants expired, weighted average exercise price (in dollars per share)
Outstanding warrants (in shares)	8,588,000		8,588,000
Outstanding warrants, weighted-average exercise price (in dollars per share)	$ 1.09		$ 1.09