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, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Weighted average grant-date fair value of options granted during the period (in dollars per share)	$ 1.51	$ 2.64	$ 1.76	$ 2.89
Options in-the-money (in shares) (in shares)	215,942	706,620	215,942	706,620
Aggregate intrinsic value of options exercised during the period	$ 1.02	$ 1.02	$ 1.18	$ 2.20