Note 1 - Significant Accounting Policies (Tables)

3 Months Ended

Mar. 31, 2019

Notes Tables

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

	March 31, 2019
	Amortized Cost		Accrued Interest		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Obligations of the U.S. Government and its agencies	$	46,201	$	183	$	31	$	(55	)	$	46,360
Corporate debt securities		34,316		226		15		(81	)		34,476
Certificates of deposit		3,559		12		6		(5	)		3,572
Total investments	$	84,076	$	421	$	52	$	(141	)	$	84,408

	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]

	March 31, 2019		December 31, 2018
Maturing in one year or less	$	72,753	$	77,736
Maturing after one year through two years		11,655		22,376
Total investments	$	84,408	$	100,112

Schedule of Receivables from Collaborations [Table Text Block]

	March 31, 2019
	Billed		Unbilled		Total
U.S. Department of Health and Human Services	$	673		1,014		1,687
Shionogi & Co. Ltd.		1,451		—		1,451
Green Cross Corporation		642		—		642
Mundipharma International Holdings Limited		21		—		21
Seqirus UK Limited		1,175		26		1,201
Total receivables	$	3,962	$	1,040	$	5,002

	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]

	2019		2018
Product sales	$	1,679	$	—
Royalty revenues		2,322		3,661
Collaborative and other research and development revenues:
U.S. Department of Health and Human Services		1,886		315
Total collaborative and other research and development revenues		1,886		315
Total revenues	$	5,887	$	3,976