Note 16 - Stock-Based Compensation - Stock Purchase Plan (Details) - Employee Stock Purchase Plan - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Shares granted (in shares)	38,738	29,882	17,305
Issuance of shares of common stock as a result of stock purchased under the Employee Stock Purchase Plan (in shares)	37,114	28,775	15,528
Weighted average fair value per share granted (in dollars per share)	$ 6.01	$ 4.81	$ 6.63