Note 16 - Income Taxes (Tables)

12 Months Ended

Dec. 31, 2019

Notes Tables

Schedule of Deferred Tax Assets [Table Text Block]

	December 31, 201 9			December 31, 201 8
Deferred tax assets:
Accruals and other	$	3,672		$	3,263
Research credits		7,275			7,275
Net operating loss carryforward		52,361			39,082
Section 59(e) R&D expenditures		8,933			10,387
Deferred revenue		21,324			20,689
Total deferred tax assets		93,565			80,696
Valuation allowance		(93,565	)		(80,696	)
Net deferred tax assets	$	—		$	—

Schedule of Effective Income Tax Rate Reconciliation [Table Text Block]

	Year Ended December 31,
	201 9			2018			2017
Tax at statutory federal rate	$	(11,180	)	$	(9,901	)	$	(17,751	)
State tax—net of federal benefit		(2,538	)		(792	)		350
General business credits		—			(500	)		(316	)
Stock options		800			1,048			42
Other		7			295			(19	)
Change in valuation allowance		12,914			9,852			(17,110	)
Tax reform – tax rate change		—			—			34,103
Provision (benefit) for income taxes	$	3		$	2		$	(701	)

Schedule of Unrecognized Tax Benefits Roll Forward [Table Text Block]

	Year Ended December 31,
	2019		2018		2017
Unrecognized benefit—beginning of period	$	2,635	$	2,365	$	2,162
Gross increases—prior period tax positions		—		57		—
Gross increases—current period tax positions		—		213		203
Unrecognized benefit—end of period	$	2,635	$	2,635	$	2,365