Note 4 - Share-based Compensation - Stock Options Issued Outside of the 2007 Equity Incentive Plan (Details) - Outside of the 2007 Plan [Member] - $ / shares	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Weighted average price per share, ending balance (in dollars per share)	$ 0.41	$ 0.41
Options outstanding, beginning balance (in shares)	20,148,766	19,394,975
Weighted average price per share, beginning balance (in dollars per share)	$ 0.43	$ 0.40
Options outstanding, granted (in shares)	4,552,201	484,077
Weighted average price per share, granted (in dollars per share)	$ 0.47	$ 0.38
Options outstanding, exercised (in shares)	3,866,630	(60,000)
Options outstanding, expired (in shares)	(3,866,629)
Exercise price per share, expired (in dollars per share)	$ 0.18
Weighted average price per share, expired (in dollars per share)	$ 0.18
Exercise of stock options (in shares)	(3,866,630)	60,000
Exercised, exercise price per share (in dollars per share)	$ 0.18	$ 0.25
Weighted average price per share, exercised (in dollars per share)	$ 0.18	$ 0.25
Options outstanding, ending balance (in shares)	16,967,708	19,819,052
Minimum [Member]
Exercise price per share, beginning balance (in dollars per share)	$ 0.18	$ 0.18
Granted, exercise price per share (in dollars per share)	0.43	0.33
Exercised, exercise price per share (in dollars per share)
Exercise price per share, ending balance (in dollars per share)	0.18	0.18
Maximum [Member]
Exercise price per share, beginning balance (in dollars per share)	1	1
Granted, exercise price per share (in dollars per share)	0.67	0.45
Exercised, exercise price per share (in dollars per share)
Exercise price per share, ending balance (in dollars per share)	$ 1	$ 1