Note 16 - Stock-Based Compensation - Stock Purchase Plan (Details) - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Issuance of shares of common stock as a result of stock purchased under the Employee Stock Purchase Plan (in shares)	28,775
Employee Stock Purchase Plan
Shares granted (in shares)	29,882	17,305	12,414
Issuance of shares of common stock as a result of stock purchased under the Employee Stock Purchase Plan (in shares)	28,775	15,528	13,318
Weighted average fair value per share granted (in dollars per share)	$ 4.81	$ 6.63	$ 6.42