Note 10 - Share Option and Equity Incentive Plan - Unvested Share Option Activity (Details) - $ / shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Number of unvested share options outstanding (in shares)	1,124,443
Number of unvested share options outstanding, weighted-average grant date fair value (in dollars per share)	$ 6.53
Number of share options granted (in shares)	749,964
Number of unvested share options granted, weighted-average grant date fair value (in dollars per share)	$ 4.53	$ 6.33	$ 9.32
Number of unvested share options vested (in shares)	(479,295)
Number of unvested share options vested, weighted-average grant date fair value (in dollars per share)	$ 5.92
Number of unvested share options forfeited (in shares)	(216,510)
Number of unvested share options forfeited, weighted-average grant date fair value (in dollars per share)	$ 6.08
Number of unvested share options outstanding (in shares)	1,178,602	1,124,443
Number of unvested share options outstanding, weighted-average grant date fair value (in dollars per share)	$ 5.61	$ 6.53