Note 6 - Share-based Compensation - Stock Options Issued Under the 2007 Equity Incentive Plan (Details) - The 2007 Equity Incentive Plan [Member] - $ / shares	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016
Options outstanding, Balance (in shares)	9,831,586	9,916,586
Exercise price per share, Balance (in dollars per share)
Weighted average price per share, Balance (in dollars per share)	$ 0.43	$ 0.47	0.44	0.44
Options outstanding, granted (in shares)		300,000
Exercise price per share, granted (in dollars per share)		$ 0.69
Weighted average price per share, granted (in dollars per share)		$ 0.69
Options outstanding, expired (in shares)	(50,000)
Exercise price per share,Expired (in dollars per share)	$ 1.89
Weighted average price per share, expired (in dollars per share)	$ 1.89
Options outstanding, Balance (in shares)	9,781,586	10,216,586
Minimum [Member]
Exercise price per share, Balance (in dollars per share)	$ 0.23	$ 0.23	0.23	0.23
Exercise price per share, granted (in dollars per share)
Exercise price per share,Expired (in dollars per share)
Maximum [Member]
Exercise price per share, Balance (in dollars per share)	1.65	1.89	$ 1.89	$ 1.89
Exercise price per share, granted (in dollars per share)
Exercise price per share,Expired (in dollars per share)