Note 1 - Significant Accounting Policies and Concentrations of Risk - Summary of Revenues (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenues	$ 4,016,000	$ 6,102,000	$ 2,871,000	$ 4,823,000	$ 39,725,000	$ 1,775,000	$ 1,448,000	$ 5,887,000	$ 17,812,000	$ 48,835,000	$ 20,653,000
Torii Pharmaceutical Co. [Member]
Revenues										20,101,000
Product [Member]
Revenues									3,301,000	17,533,000
Royalty [Member]
Revenues									3,381,000	6,303,000	6,101,000
Collaborative and Other Research and Development [Member]
Revenues									11,130,000	24,999,000	14,552,000
Collaborative and Other Research and Development [Member] | US Department of Health and Human Services [Member]
Revenues									9,231,000	4,898,000	2,552,000
Collaborative and Other Research and Development [Member] | Torii Pharmaceutical Co. [Member]
Revenues									$ 1,899,000	$ 20,101,000
Collaborative and Other Research and Development [Member] | Seqirus UK Limited [Member]
Revenues											$ 12,000