Note 10 - Stock-based Compensation - Changes in Shares Under Option Plans (Details) - $ / shares	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Beginning balance (in shares)	298,740	759,683
Beginning balance (in dollars per share)	$ 9.97	$ 11.36
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross	1,500
Issued (in dollars per share)	$ 49.91
Exercised (in shares)	(22,669)	(369,952)
Exercised (in dollars per share)	$ 12.82	$ 12.70
Forfeited (in shares)	(1,100)	(1,650)
Forfeited (in dollars per share)	$ 15.48	$ 15.48
Expired (in shares)	(6,037)	(8,007)
Expired (in dollars per share)	$ 13.57	$ 16.90
Ending balance (in shares)	270,434	380,074
Ending balance (in dollars per share)	$ 9.85	$ 9.92