Note 10 - Share Option and Equity Incentive Plan - Stock Option Activity (Details) - $ / shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Number of share options outstanding (in shares)	2,425,426
Number of share options outstanding, weighted average exercise price (in dollars per share)	$ 9.03
Number of share options granted (in shares)	749,964
Weighted-average exercise price ($) (in dollars per share)	$ 10.29
Number of share options exercised (in shares)	(85,943)	(41,222)	(65,054)
Number of share options exercised, weighted average exercise price (in dollars per share)	$ 0.82
Number of share options forfeited (in shares)	(239,667)
Number of share options forfeited, weighted average exercise price (in dollars per share)	$ 14.27
Number of share options oustanding (in shares)	2,849,780	2,425,426
Number of share options oustanding, weighted average exercise price (in dollars per share)	$ 9.15	$ 9.03
Number of share options vested or expected to vest (in shares)	2,790,851
Number of share options vested or expected to vest, weighted average exercise price (in dollars per share)	$ 9.08
Number of share options exercisable (in shares)	1,671,179
Number of share options exercisable, weighted average exercise price (in dollars per share)	$ 6.81