Note 1 - Significant Accounting Policies (Tables)

9 Months Ended

Sep. 30, 2018

Notes Tables

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

	September 30, 2018
	Amortized Cost		Accrued Interest		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Obligations of the U.S. Government and its agencies	$	51,436	$	170	$	—	$	(188	)	$	51,418
Corporate debt securities		40,893		244		—		(207	)		40,930
Certificates of deposit		4,543		18		—		(15	)		4,546
Total investments	$	96,872	$	432	$	—	$	(410	)	$	96,894

	December 31, 2017
	Amortized Cost		Accrued Interest		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Obligations of the U.S. Government and its agencies	$	60,121	$	177	$	—	$	(122	)	$	60,176
Corporate debt securities		34,021		203		—		(108	)		34,116
Certificates of deposit		11,099		32		1		(14	)		11,118
Total investments	$	105,241	$	412	$	1	$	(244	)	$	105,410

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

	2018		2017
Maturing in one year or less	$	67,737	$	64,115
Maturing after one year through two years		29,157		34,257
Maturing after two years		—		7,038
Total investments	$	96,894	$	105,410

Schedule of Receivables from Collaborations [Table Text Block]

	September 30, 2018
	Billed		Unbilled		Total
U.S. Department of Health and Human Services	$	403	$	1,289	$	1,692
Shionogi & Co. Ltd.		35		—		35
Green Cross Corporation		313		27		340
Mundipharma International Holdings Limited		75		—		75
Seqirus UK Limited		1,252		—		1,252
Total receivables	$	2,078	$	1,316	$	3,394

	December 31, 2017
	Billed		Unbilled		Total
U.S. Department of Health and Human Services	$	42	$	2,020	$	2,062
Shionogi & Co. Ltd.		1,600		—		1,600
Green Cross Corporation		1,388		28		1,416
Mundipharma International Holdings Limited		47		—		47
Seqirus UK Limited		825		167		992
Total receivables	$	3,902	$	2,215	$	6,117

Schedule of New Accounting Pronouncements and Changes in Accounting Principles [Table Text Block]

	Balance at December 31, 2017			Adjustments due to ASC 606			Balance at January 1, 2018
Assets
Deferred collaboration expense	$	210		$	(58	)	$	152
Liabilities
Deferred revenue	$	8,484		$	(1,184	)	$	7,300
Equity
Accumulated deficit	$	(631,843	)	$	1,126		$	(630,717	)

	September 30, 2018
	As Reported			Adjustments due to ASC 606		Balances without adoption of ASC 606
Assets
Deferred collaboration expense	$	8		$	19	$	27
Liabilities
Deferred revenue	$	200		$	396	$	596
Equity
Accumulated deficit	$	(704,537	)	$	378	$	(704,159	)

	For the Three Months Ended September 30, 2018
	As Reported			Adjustments due to ASC 606		Balances without adoption of ASC 606
Collaborative and other research and development revenue	$	931		$	296	$	1,227
Research and development expenses		22,006			14		22,021
Net loss		(29,597	)		282		(29,315	)
Basic and diluted net loss per share	$	(0.28	)	$	0.00	$	(0.28	)

	For the Nine Months Ended September 30, 2018
	As Reported			Adjustments due to ASC 606		Balances without adoption of ASC 606
Collaborative and other research and development revenue	$	13,598		$	888	$	14,486
Research and development expenses		61,457			44		61,501
Net loss		(73,820	)		846		(72,974	)
Basic and diluted net loss per share	$	(0.73	)	$	0.01	$	(0.72	)

Disaggregation of Revenue [Table Text Block]

	Three Months				Nine Months
	2018		2017		2018		2017
Product sales	$	—	$	1,501	$	—	$	1,501
Royalty revenue		523		442		4,326		7,252
Collaborative and other research and development revenues:
U.S. Department of Health and Human Services		931		1,490		1,598		4,305
Shionogi & Co. Ltd.		—		296		—		888
Seqirus UK Limited		—		5,031		12,000		7,350
Total collaborative and other research and development revenues		931		6,817		13,598		12,543
Total revenues	$	1,454	$	8,760	$	17,924	$	21,296