Note 9 - Options and Warrants to Purchase Common Stock - Summary of the Status and Changes of the Warrants (Details)	3 Months Ended
	Mar. 31, 2018 $ / shares shares
Outstanding at begin of year, warrant (in shares) | shares	18,813,373
Outstanding at begin of year, warrant, weighted average price (in dollars per share) | $ / shares	$ 0.14
Issued, warrant (in shares) | shares
Issued, warrant, weighted average price (in dollars per share) | $ / shares
Exercised, warrant (in shares) | shares	(500,000)
Exercised, warrant, weighted average price (in dollars per share) | $ / shares	$ 0.04
Forfeited, warrant (in shares) | shares
Forfeited, warrant, weighted average price (in dollars per share) | $ / shares
Outstanding at end of year, warrant (in shares) | shares	18,313,373
Outstanding at end of year, warrant, weighted average price (in dollars per share) | $ / shares	$ 0.14