Note 12 - Share Option and Equity Incentive Plans - Unvested Share Option Activity (Details) - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Number of unvested share options outstanding (in shares)	1,161,530
Number of unvested share options outstanding, weighted-average grant date fair value (in dollars per share)	$ 6.06
Number of share options granted (in shares)	495,460
Number of unvested share options granted, weighted-average grant date fair value (in dollars per share)	$ 7.23	$ 6.15
Number of unvested share options vested (in shares)	(408,196)
Number of unvested share options vested, weighted-average grant date fair value (in dollars per share)	$ 5.94
Number of unvested share options forfeited (in shares)	(254,283)
Number of unvested share options forfeited, weighted-average grant date fair value (in dollars per share)	$ 14.10
Number of unvested share options outstanding (in shares)	994,511	1,161,530
Number of unvested share options outstanding, weighted-average grant date fair value (in dollars per share)	$ 6.59	$ 6.06