Note 9 - Options and Warrants to Purchase Common Stock - Summary of the Status and Changes of the Options Granted Under the Stock Option Plans and Other Agreements (Details)	3 Months Ended
	Mar. 31, 2018 $ / shares shares
Outstanding at December 31, 2017 (in shares) | shares	57,057,768
Outstanding at December 31, 2017 (in dollars per share) | $ / shares	$ 0.36
Granted (in shares) | shares	3,000,000
Granted (in dollars per share) | $ / shares	$ 0.12
Exercised (in shares) | shares
Exercised (in dollars per share) | $ / shares
Forfeited (in shares) | shares	(232,645)
Forfeited (in dollars per share) | $ / shares	$ 1.36
Outstanding at March 31, 2018 (in shares) | shares	59,825,123
Outstanding at March 31, 2018 (in dollars per share) | $ / shares	$ 0.35