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)	6 Months Ended
	Jun. 30, 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	4,224,999
Granted (in dollars per share) | $ / shares	$ 0.11
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 June 30, 2018 (in shares) | shares	61,050,122
Outstanding at June 30, 2018 (in dollars per share) | $ / shares	$ 0.34