Note 1 - Significant Accounting Policies (Tables)

6 Months Ended

Jun. 30, 2019

Notes Tables

Debt Securities, Available-for-sale [Table Text Block]

	June 30, 2019
	Amortized Cost		Accrued Interest		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Obligations of the U.S. Government and its agencies	$	32,488	$	144	$	50	$	(13	)	$	32,669
Corporate debt securities		25,731		147		24		(27	)		25,875
Certificates of deposit		3,559		18		8		(1	)		3,584
Total investments	$	61,778	$	309	$	82	$	(41	)	$	62,128

	December 31, 2018
	Amortized Cost		Accrued Interest		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Obligations of U.S. Government and its agencies	$	50,613	$	176	$	15	$	(131	)	$	50,673
Corporate debt securities		45,793		254		4		(171	)		45,880
Certificates of deposit		3,559		14		—		(14	)		3,559
Total investments	$	99,965	$	444	$	19	$	(316	)	$	100,112

Available For Sale Securities Debt Maturities Fair Value [Table Text Block]

	June 30, 2019		December 31, 2018
Maturing in one year or less	$	61,387	$	77,736
Maturing after one year through two years		741		22,376
Total investments	$	62,128	$	100,112

Schedule of Receivables from Collaborations [Table Text Block]

	June 30, 2019
	Billed		Unbilled		Total
U.S. Department of Health and Human Services	$	998	$	989	$	1,987
Shionogi & Co. Ltd.		96		—		96
Green Cross Corporation		542		—		542
Mundipharma International Holdings Limited		49		—		49
Seqirus UK Limited		902		26		928
Total receivables	$	2,587	$	1,015	$	3,602

	December 31, 2018
	Billed		Unbilled		Total
U.S. Department of Health and Human Services	$	—	$	1,525	$	1,525
Shionogi & Co. Ltd.		854		—		854
Green Cross Corporation		876		28		904
Mundipharma International Holdings Limited		44		—		44
Seqirus UK Limited		940		26		966
Total receivables	$	2,714	$	1,579	$	4,293

Disaggregation of Revenue [Table Text Block]

	Three Months				Six Months
	2019		2018		2019		2018
Product sales	$	—	$	—	$	1,679	$	—
Royalty revenue		696		142		3,018		3,803
Collaborative and other research and development revenues:
U.S. Department of Health and Human Services		752		352		2,638		667
Seqirus UK Limited		—		12,000		—		12,000
Total collaborative and other research and development revenues		752		12,352		2,638		12,667
Total revenues	$	1,448	$	12,494	$	7,335	$	16,470