Note 7 - Liabilities Related to Sale of Future Royalties - Deferred Revenue Activity (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Current portion	$ (2,779)	$ (2,916)
Long-term portion	12,150	$ 13,416
HealthCare Royalty Partners III, L.P. [Member] | Royalty Arrangement [Member]
Total liability related to sale of future royalties, start of year	16,332
Non-cash royalty revenue paid to HCRP	(3,277)
Non-cash interest expense recognized	1,874
Total liability related to sale of future royalties, end of year	14,929
Current portion	(2,779)
Long-term portion	$ 12,150