Note 3 - Collaborative and Other Research and Development Contracts (Details Textual) - USD ($) $ in Thousands				1 Months Ended			9 Months Ended	42 Months Ended
	Sep. 06, 2018	Jun. 16, 2015	Feb. 28, 2006	Sep. 30, 2013	Jun. 30, 2006	Jun. 30, 2000	Sep. 30, 2018	Sep. 30, 2018	Mar. 31, 2015
Centers for Disease Control and Prevention [Member]
Collaborative Agreement Contract Value	$ 34,660
Contract Term	5 years
CSL Limited [Member
Proceeds from License Fees Received		$ 33,740
Milestone Payment Received		7,000
Milestone Payment Maximum		$ 5,000
Royalty Term		10 years
National Institute of Allergy and Infectious Diseases [Member]
Collaborative Agreement Contract Value				$ 5,000
Expected Receivable From Awards for Research and Development Contracts							$ 43,035
UAB [Member]
Period of Agreement							25 years
Renewable Period of Agreement							5 years
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]
Upfront Payments Receivable Amount			$ 10,000
AECOM and IRL [Member]
Milestone Payment Maximum						$ 4,000
Milestone Payment Minimum						1,400
Annual License Fee Minimum						150
Annual License Fee Maximum						$ 500
Advance Notice Period for Termination of Agreement						60 days