Note 5 - Share-based Compensation - Stock Options Issued Under the 2007 Equity Incentive Plan (Details) - The 2007 Equity Incentive Plan [Member] - $ / shares		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018
Options outstanding, balance (in shares)		9,691,586	9,831,586
Exercise price per share, balance (in dollars per share)		$ 0.94	$ 1.89
Options outstanding, expired (in shares)		(922,135)	(140,000)
Exercise price per share, expired (in dollars per share)		$ 0.55	$ 1.89
Options outstanding, balance (in shares)		8,769,451	9,691,586
Exercise price per share, balance (in dollars per share)		$ 0.94	$ 0.94
Weighted average exercise price per share, balance (in dollars per share)	[1]
Minimum [Member]
Exercise price per share, balance (in dollars per share)		0.22	0.22
Exercise price per share, expired (in dollars per share)		0.45	0.35
Exercise price per share, balance (in dollars per share)		0.23	0.22
Maximum [Member]
Exercise price per share, balance (in dollars per share)		0.43	0.44
Exercise price per share, expired (in dollars per share)		0.49	1.41
Exercise price per share, balance (in dollars per share)		$ 0.43	$ 0.43

[1] Aggregate intrinsic value based on closing common stock price of $0.24 at December 31, 2018.