Note 7 - Stockholders' Equity - Warrants (Details)	6 Months Ended
	Jun. 30, 2021 $ / shares shares
Balance, beginning (in shares) | shares	2,424,724
Balance, beginning, weighted average exercise price (in dollars per share) | $ / shares	$ 6.36
Warrants for common stock sold (in shares) | shares	0
Warrants for common stock sold, weighted average exercise price (in dollars per share) | $ / shares	$ 0
Warrants for common stock exercised (in shares) | shares	0
Warrants for common stock exercised, weighted average exercise price (in dollars per share) | $ / shares	$ 0
Balance, ending (in shares) | shares	2,424,724
Balance, ending, weighted average exercise price (in dollars per share) | $ / shares	$ 6.36