Note 6 - Liabilities Related to Sale of Future Royalties - Deferred Revenue Activity (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Current portion	$ (3,150)	$ (2,916)
Long-term portion	11,319	$ 13,416
HealthCare Royalty Partners III, L.P. [Member] | Royalty Arrangement [Member]
Total liability related to sale of future royalties, start of period	16,332
Non-cash royalty revenue paid to HCRP	(2,800)
Non-cash interest expense recognized	937
Total liability related to sale of future royalties, end of period	14,469
Current portion	(3,150)
Long-term portion	$ 11,319