Note 9 - Options and Warrants to Purchase Common Stock - Summary of the Status and Changes of the Warrants (Details)	6 Months Ended
	Jun. 30, 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	8,000,000
Issued, warrant, weighted average price (in dollars per share) | $ / shares	$ 0.15
Exercised, warrant (in shares) | shares	(2,000,000)
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	24,813,373
Outstanding at end of year, warrant, weighted average price (in dollars per share) | $ / shares	$ 0.15