Note 1 - Significant Accounting Policies - Summary of Revenues (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Revenues	$ 1,454	$ 8,760	$ 17,924	$ 21,296
Product [Member]
Revenues		1,501		1,501
Royalty [Member]
Revenues	523	442	4,326	7,252
Collaborative and Other Research and Development [Member]
Revenues	931	6,817	13,598	12,543
Collaborative and Other Research and Development [Member] | US Department of Health and Human Services [Member]
Revenues	931	1,490	1,598	4,305
Collaborative and Other Research and Development [Member] | Shionogi and Co. Ltd [Member]
Revenues		296		888
Collaborative and Other Research and Development [Member] | Seqirus UK Limited [Member]
Revenues		$ 5,031	$ 12,000	$ 7,350