Note 10 - Stock-based Compensation - Changes in Shares Under Option Plans (Details) - $ / shares	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Beginning balance (in shares)	216,859	298,740
Beginning balance (in dollars per share)	$ 8.80	$ 9.97
Issued (in shares)
Issued (in dollars per share)
Exercised (in shares)	(2,675)	(16,759)
Exercised (in dollars per share)	$ 24.67	$ 11.80
Forfeited (in shares)		(1,100)
Forfeited (in dollars per share)		$ 15.48
Expired (in shares)		(6,037)
Expired (in dollars per share)		$ 13.57
Ending balance (in shares)	214,184	274,844
Ending balance (in dollars per share)	$ 8.60	$ 9.76