Note 4 - Share-based Compensation - Stock Options Issued Under the 2007 Equity Incentive Plan (Details) - The 2007 Equity Incentive Plan [Member] - $ / shares	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Weighted average price per share, beginning balance (in dollars per share)	$ 0.44	$ 0.44
Weighted average price per share, ending balance (in dollars per share)	$ 0.44	$ 0.44
Options outstanding, beginning balance (in shares)	9,916,586	10,241,086
Shares available, beginning balance (in shares)	1,981,414	1,758,914
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross	340,000	40,000
Shares available, granted (in shares)	(340,000)	(40,000)
Exercise price per share, granted (in dollars per share)		$ 0.45
Weighted average price per share, granted (in dollars per share)	$ 0.65	$ 0.45
Options outstanding, ending balance (in shares)	10,256,586	10,281,086
Shares available, ending balance (in shares)	1,641,414	1,718,914
Minimum [Member]
Exercise price per share, beginning balance (in dollars per share)	$ 0.23	$ 0.23
Exercise price per share, granted (in dollars per share)	0.39
Exercise price per share, ending balance (in dollars per share)	0.23	0.23
Maximum [Member]
Exercise price per share, beginning balance (in dollars per share)	1.89	1.89
Exercise price per share, granted (in dollars per share)	0.69
Exercise price per share, ending balance (in dollars per share)	$ 1.89	$ 1.89