Note 11 - Collaborative and Other Research and Development Contracts (Details Textual) - USD ($) $ in Thousands						1 Months Ended			3 Months Ended								6 Months Ended	12 Months Ended			67 Months Ended	69 Months Ended
	Sep. 03, 2020	Mar. 04, 2020	Nov. 05, 2019	Sep. 06, 2018	Jun. 16, 2015	Aug. 31, 2020	Jun. 30, 2006	Jun. 30, 2000	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2020	Dec. 31, 2020	Mar. 31, 2015	Nov. 11, 2011
Revenue from Contract with Customer, Including Assessed Tax									$ 4,016	$ 6,102	$ 2,871	$ 4,823	$ 39,725	$ 1,775	$ 1,448	$ 5,887		$ 17,812	$ 48,835	$ 20,653
Arbitration Proceedings of SUL Agreement [Member]
Litigation Settlement, Amount Awarded from Other Party		$ 5,000
Arbitration Proceedings of SUL Agreement [Member] | Other Income [Member]
Gain (Loss) Related to Litigation Settlement, Total																		8,893
Arbitration Proceedings of SUL Agreement [Member] | Selling, General and Administrative Expenses [Member]
Legal Fees																	$ 5,026
US Department of Health and Human Services [Member]
Collaborative Agreement Contract Value				$ 34,660
Contract Term (Year)				5 years
Proceeds from Collaborators	$ 6,932																		13,864
Torii Pharmaceutical Co. [Member]
Upfront Payments Receivable Amount			$ 22,000
Potential Milestone Payments Receivable if Regulatory Approval Before December 31, 2021			$ 15,000
Maximum Customary Reduction on Royalty Rate			50.00%
Royalty Payments Receivable, Expiration Term From First Commercial (Year)			10 years
Revenue from Contract with Customer, Including Assessed Tax																			20,101
Contract with Customer, Liability, Revenue Recognized																		1,899
Torii Pharmaceutical Co. [Member] | License [Member]
Revenue from Contract with Customer, Including Assessed Tax																			$ 19,344
Torii Pharmaceutical Co. [Member] | Service [Member]
Revenue from Contract with Customer, Including Assessed Tax																		757
Torii Pharmaceutical Co. [Member] | Minimum [Member]
Royalty Rate if Maintains Sakigake Designation			20.00%
Torii Pharmaceutical Co. [Member] | Maximum [Member]
Royalty Rate if Maintains Sakigake Designation			40.00%
CSL Limited [Member
Proceeds from License Fees Received					$ 33,740
Milestone Payment Received																					$ 12,000
Base Contract [Member]
Government Contract Receivable																							$ 16,265
Additional Development Options [Member]
Government Contract Receivable																							22,855
ASPRBARDA Contract [Member]
Government Contract Receivable																							$ 39,120
Proceeds from awards for Research and Development Contracts																						$ 20,574
Green Cross Corporation [Member]
Proceeds from License Fees Received							$ 250
Mundipharma [Member]
Potential Milestone Payments Receivable																								$ 15,000
AECOM and IRL [Member]
Milestone Payment Minimum								$ 1,400
Milestone Payment Maximum								4,000
Annual License Fee Minimum								150
Annual License Fee Maximum								$ 500
National Institute of Allergy and Infectious Diseases [Member]
Expected Receivable From Awards for Research and Development Contracts																		$ 45,931
Collaborative Agreement Contract, Covenant, Maximum Amount of Funding						$ 43,908
Collaborative Agreement Contract Value						$ 6,326
UAB [Member]
Period of Agreement (Year)																		25 years
Renewable Period of Agreement (Year)																		5 years