Note 6 - Shareholders' Equity - Summary of Certain Additional Information about Stock Options (Details) - Share-Based Payment Arrangement, Option [Member] - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Weighted average grant-date fair value of options granted during the period (in dollars per share)	$ 0.90	$ 1.51	$ 1.60	$ 1.76
Options in-the-money (in shares) (in shares)	221,417	215,942	221,417	215,942
Aggregate intrinsic value of options exercised during the period	$ 0	$ 1.02	$ 6,839	$ 1.18