Note 15 - Stock-based Compensation - Stock Purchase Plan (Details) - Employee Stock Purchase Plan [Member] - $ / shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Shares granted (in shares)	18,711	23,408	24,811
Proceeds from issuance of common stock, Employee Stock Purchase Plan, Shares (in shares)	20,192	24,033	25,321
Weighted average fair value per share granted (in dollars per share)	$ 3.28	$ 2.39	$ 2.37