Note 4 - Stock-based Compensation - Stock Option Activity (Details)	3 Months Ended
	Mar. 31, 2021 $ / shares shares	Mar. 31, 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	(750)	0
Exercised, Weighted Average Exercise Price (in dollars per share) | $ / shares	$ 8.91
Expired and forfeited, Shares (in shares) | shares
Expired and forfeited, Weighted Average Exercise Price (in dollars per share) | $ / shares
Outstanding, Shares (in shares) | shares	26,750
Outstanding, Weighted Average Exercise Price (in dollars per share) | $ / shares	$ 8.61
Exercisable, Shares (in shares) | shares	7,915
Exercisable, Weighted Average Exercise Price (in dollars per share) | $ / shares	$ 7.73