Note 10 - Stock-based Compensation Expense - Non-vested Stock Options (Details) - $ / shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Nonvested (in shares)	12,000	25,000
Nonvested, weighted average grant date fair value (in dollars per share)	$ 1.07	$ 1.40
Granted (in shares)	6,000	10,000
Granted, weighted average grant date fair value (in dollars per share)	$ 1.10	$ 0.78
Vested (in shares)	(9,000)	(23,000)
Vested, weighted average grant date fair value (in dollars per share)	$ 0.91	$ 1.22
Nonvested (in shares)	9,000	12,000
Nonvested, weighted average grant date fair value (in dollars per share)	$ 1.10	$ 1.07