Note 7 - Liabilities Related to the Sale of Future Royalties - Deferred Revenue Activity (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Current portion	$ (2,916)	$ (3,328)
Long-term portion	13,416	$ 14,413
HealthCare Royalty Partners III, L.P. [Member] | Royalty Arrangement [Member]
Total liability related to the sale of future royalties, start of year	17,741
Non-cash royalty revenue paid to HCRP	(3,482)
Non-cash interest expense recognized	2,073
Total liability related to the sale of future royalties, end of year	16,332
Current portion	(2,916)
Long-term portion	$ 13,416