Note 4 - Stock-based Compensation - Stock Option Activity (Details)	6 Months Ended
	Jun. 30, 2021 $ / shares shares	Jun. 30, 2020 shares
Outstanding, Shares (in shares) | shares	17,500
Outstanding, Weighted Average Exercise Price (in dollars per share) | $ / shares	$ 6.97
Granted, Shares (in shares) | shares	10,000	10,000
Granted, Weighted Average Exercise Price (in dollars per share) | $ / shares	$ 11.50
Exercised, Shares (in shares) | shares	(3,000)	0
Exercised, Weighted Average Exercise Price (in dollars per share) | $ / shares	$ 9.23
Expired and forfeited, Shares (in shares) | shares	(1,000)
Expired and forfeited, Weighted Average Exercise Price (in dollars per share) | $ / shares	$ 10.75
Outstanding, Shares (in shares) | shares	23,500
Outstanding, Weighted Average Exercise Price (in dollars per share) | $ / shares	$ 8.45
Exercisable, Shares (in shares) | shares	5,165
Exercisable, Weighted Average Exercise Price (in dollars per share) | $ / shares	$ 6.54