Note 9 - Share Based Payments - Non-vested Stock Options (Details) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Non-vested stock options, shares (in shares)	2,137,000	1,340,000
Non-vested stock options, Weighted average fair value (in dollars per share)	$ 0.13	$ 0.34
Options granted, shares (in shares)	250,000	2,557,000
Options granted, Weighted average fair value (in dollars per share)	$ 0.47	$ 0.10
Vested during period, shares (in shares)	(1,231,000)
Vested during period, Weighted average fair value (in dollars per share)	$ (0.13)
Options cancelled, shares (in shares)	(17,500)	(1,760,000)
Options cancelled, Weighted average fair value (in dollars per share)	$ (0.13)	$ (0.29)
Non-vested shares under option, shares (in shares)	1,138,500	2,137,000
Non-vested shares under option, Weighted average fair value (in dollars per share)	$ 0.20	$ 0.13