Note 9 - Stockholders' Equity - Summary of Information Concerning Outstanding and Exercisable Stock Options (Details)	3 Months Ended
	Mar. 31, 2021 $ / shares shares
Number of outstanding (in shares)	6,810,750
Number of exercisable (in shares)	3,316,650
Range 1 [Member]
Range of exercise prices per share (in dollars per share) | $ / shares	$ 0.33
Number of outstanding (in shares)	2,645,000
Number of exercisable (in shares)	87,000
Expiry date	Jun. 30, 2025
Range 2 [Member]
Range of exercise prices per share (in dollars per share) | $ / shares	$ 0.39
Number of outstanding (in shares)	1,035,000
Number of exercisable (in shares)	135,000
Expiry date	Feb. 01, 2026
Range 3 [Member]
Range of exercise prices per share (in dollars per share) | $ / shares	$ 0.40
Number of outstanding (in shares)	620,000
Number of exercisable (in shares)	620,000
Expiry date	Dec. 20, 2021
Range 4 [Member]
Range of exercise prices per share (in dollars per share) | $ / shares	$ 0.42
Number of outstanding (in shares)	522,750
Number of exercisable (in shares)	486,650
Expiry date	Nov. 08, 2022
Range 5 [Member]
Range of exercise prices per share (in dollars per share) | $ / shares	$ 0.42
Number of outstanding (in shares)	713,000
Number of exercisable (in shares)	713,000
Expiry date	Jun. 04, 2023
Range 6 [Member]
Range of exercise prices per share (in dollars per share) | $ / shares	$ 0.50
Number of outstanding (in shares)	1,275,000
Number of exercisable (in shares)	1,275,000
Expiry date	Jun. 04, 2023