Note 8 - Stockholders' Equity - Activity of Stock Option Plan (Details)	6 Months Ended
	Jun. 30, 2017 $ / shares shares
Outstanding, options (in shares) | shares	3,499,475
Outstanding, weighted average exercise price, options (in dollars per share) | $ / shares	$ 1.21
Granted, options (in shares) | shares
Granted, weighted average exercise price, options (in dollars per share) | $ / shares
Forfeited or expired, options (in shares) | shares	(115,200)
Forfeited or expired, weighted average exercise price, options (in dollars per share) | $ / shares	$ 17.75
Outstanding, options (in shares) | shares	3,384,275
Outstanding, weighted average exercise price, options (in dollars per share) | $ / shares	$ 0.64
Exercisable, options (in shares) | shares	1,135,494
Exercisable, weighted average exercise price, options (in dollars per share) | $ / shares	$ 1.77