Note 5 - Stockholders' Equity and Stock-based Compensation - Stock Option Activity (Details) - $ / shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Outstanding at beginning of year (in shares)	9,000	33,250
Outstanding, weighted average exercise price (in dollars per share)	$ 13.30	$ 9.64
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Net of Forfeitures, Total (in shares)	0	0
Granted, weighted average exercise price (in dollars per share)	$ 0	$ 0
Exercised (in shares)	(3,654)	(24,250)
Exercised, weighted average exercise price (in dollars per share)	$ 13.30	$ 8.28
Expired/Forfeited (in shares)	(5,346)	0
Expired/Forfeited, weighted average exercise price (in dollars per share)	$ 13.30	$ 0
Outstanding at end of year (in shares)	0	9,000
Outstanding, weighted average exercise price (in dollars per share)	$ 0	$ 13.30
Options exercisable at end of year (in shares)	0	9,000
Options exercisable, weighted average exercise price (in dollars per share)	$ 0	$ 13.30