Note 5 - Share-based Compensation - Stock Options Issued Outside of the 2007 Equity Incentive Plan (Details) - Outside of the 2007 Plan [Member]	9 Months Ended
	Sep. 30, 2017 $ / shares shares	Sep. 30, 2016 $ / shares shares	Dec. 31, 2016 $ / shares	Dec. 31, 2015 $ / shares
Options outstanding, Balance (in shares) | shares	20,148,766	19,394,975
Weighted average price per share, Balance (in dollars per share)	$ 0.51	$ 0.41	$ 0.40	$ 0.40
Options outstanding, granted (in shares) | shares	6,828,872	484,077
Weighted average price per share, granted (in dollars per share)	$ 0.46	$ 0.38
Options outstanding, exercised (in shares) | 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, Balance (in shares) | shares	19,244,379	19,819,052
Options outstanding, expired (in shares) | 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
Cashless exercise of stock options (in shares) | shares	(3,866,630)	60,000
Minimum [Member]
Exercise price per share, Balance (in dollars per share)	$ 0.18	$ 0.18	0.18	0.18
Exercise price per share, granted (in dollars per share)	0.43	0.33
Exercised, exercise price per share (in dollars per share)
Maximum [Member]
Exercise price per share, Balance (in dollars per share)	1	1	$ 1	$ 1
Exercise price per share, granted (in dollars per share)	0.67	$ 0.45
Exercised, exercise price per share (in dollars per share)