Note 13 - Stock Compensation Plan - Summary of Stock Options Outstanding and Exercisable by Ranges of Option Prices (Details)	12 Months Ended
	Dec. 31, 2019 $ / shares shares
Number of options outstanding (in shares) | shares	19,341,112
Number of options exercisable (in shares) | shares	13,455,439
Exercise Price Range 1 [Member]
Range of exercise prices, lower (in dollars per share)	$ 0
Range of exercise prices, upper (in dollars per share)	$ 0.10
Number of options outstanding (in shares) | shares	4,093,777
Options outstanding, weighted average remaining contractual life (Year)	4 years 313 days
Options outstanding, weighted average exercise price (in dollars per share)	$ 0.07
Number of options exercisable (in shares) | shares	3,550,111
Options exercisable, weighted average remaining contractual life (Year)	4 years 240 days
Options exercisable, weighted average exercise price (in dollars per share)	$ 0.07
Exercise Price Range 2 [Member]
Range of exercise prices, lower (in dollars per share)	0.11
Range of exercise prices, upper (in dollars per share)	$ 0.38
Number of options outstanding (in shares) | shares	15,247,335
Options outstanding, weighted average remaining contractual life (Year)	6 years 302 days
Options outstanding, weighted average exercise price (in dollars per share)	$ 0.20
Number of options exercisable (in shares) | shares	9,905,328
Options exercisable, weighted average remaining contractual life (Year)	5 years 357 days
Options exercisable, weighted average exercise price (in dollars per share)	$ 0.21