Note 6 - Share-based Compensation - Stock Options Issued Under the 2007 Equity Incentive Plan by Exercise Price Range (Details) - The 2007 Equity Incentive Plan [Member] - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Options Outstanding and Exercisable (in shares)	9,831,586	9,916,586	10,241,086
Lower Exercise Price (in dollars per share)	$ 0.22
Upper Exercise Price (in dollars per share)	$ 1.89
Weighted average remaining years contractual life (Year)	4 years
Weighted average exercise price (in dollars per share)	$ 0.44
Aggregate instrinsic value	$ 307,005
Exercise Price Range 1 [Member]
Options Outstanding and Exercisable (in shares)	100,000
Lower Exercise Price (in dollars per share)	$ 1.10
Upper Exercise Price (in dollars per share)	$ 1.89
Weighted average remaining years contractual life (Year)	182 days
Weighted average exercise price (in dollars per share)	$ 1.67
Aggregate instrinsic value
Exercise Price Range 2 [Member]
Options Outstanding and Exercisable (in shares)	892,135
Lower Exercise Price (in dollars per share)	$ 0.28
Upper Exercise Price (in dollars per share)	$ 0.99
Weighted average remaining years contractual life (Year)	1 year
Weighted average exercise price (in dollars per share)	$ 0.51
Aggregate instrinsic value	$ 6,900
Exercise Price Range 3 [Member]
Options Outstanding and Exercisable (in shares)	1,020,000
Lower Exercise Price (in dollars per share)	$ 0.25
Upper Exercise Price (in dollars per share)	$ 0.70
Weighted average remaining years contractual life (Year)	2 years
Weighted average exercise price (in dollars per share)	$ 0.55
Aggregate instrinsic value	$ 3,400
Exercise Price Range 4 [Member]
Options Outstanding and Exercisable (in shares)	3,650,528
Lower Exercise Price (in dollars per share)	$ 0.22
Upper Exercise Price (in dollars per share)	$ 0.51
Weighted average remaining years contractual life (Year)	3 years
Weighted average exercise price (in dollars per share)	$ 0.37
Aggregate instrinsic value	$ 192,206
Exercise Price Range 5 [Member]
Options Outstanding and Exercisable (in shares)	1,656,262
Lower Exercise Price (in dollars per share)	$ 0.34
Upper Exercise Price (in dollars per share)	$ 0.40
Weighted average remaining years contractual life (Year)	4 years
Weighted average exercise price (in dollars per share)	$ 0.36
Aggregate instrinsic value	$ 54,044
Exercise Price Range 6 [Member]
Options Outstanding and Exercisable (in shares)	715,161
Lower Exercise Price (in dollars per share)	$ 0.28
Upper Exercise Price (in dollars per share)	$ 0.40
Weighted average remaining years contractual life (Year)	5 years
Weighted average exercise price (in dollars per share)	$ 0.36
Aggregate instrinsic value	$ 23,455
Exercise Price Range 7 [Member]
Options Outstanding and Exercisable (in shares)	640,000
Lower Exercise Price (in dollars per share)	$ 0.30
Upper Exercise Price (in dollars per share)	$ 0.65
Weighted average remaining years contractual life (Year)	6 years
Weighted average exercise price (in dollars per share)	$ 0.48
Aggregate instrinsic value	$ 27,000
Exercise Price Range 8 [Member]
Options Outstanding and Exercisable (in shares)	477,500
Lower Exercise Price (in dollars per share)	$ 0.40
Upper Exercise Price (in dollars per share)	$ 0.60
Weighted average remaining years contractual life (Year)	7 years
Weighted average exercise price (in dollars per share)	$ 0.42
Aggregate instrinsic value
Exercise Price Range 9 [Member]
Options Outstanding and Exercisable (in shares)	340,000
Lower Exercise Price (in dollars per share)	$ 0.45
Upper Exercise Price (in dollars per share)	$ 0.57
Weighted average remaining years contractual life (Year)	8 years
Weighted average exercise price (in dollars per share)	$ 0.56
Aggregate instrinsic value
Exercise Price Range 10 [Member]
Options Outstanding and Exercisable (in shares)	340,000
Lower Exercise Price (in dollars per share)	$ 0.39
Upper Exercise Price (in dollars per share)	$ 0.69
Weighted average remaining years contractual life (Year)	9 years
Weighted average exercise price (in dollars per share)	$ 0.65
Aggregate instrinsic value