Note 15 - Income Taxes (Tables)

12 Months Ended

Dec. 31, 2016

Notes Tables

Schedule of Components of Income Tax Expense (Benefit) [Table Text Block]

	Year Ending December 31
(in thousands)	2016		2015		2014
Current
Federal	$	—	$	—	$	—
State		2		2		2
Other		—		—		—
Total current tax expense		2		2		2
Deferred
Federal		—		—		—
State		—		—		—
Other		—		—		—
Total deferred tax expense		—		—		—
Income tax provision	$	2	$	2	$	2

Schedule of Deferred Tax Assets and Liabilities [Table Text Block]

	December 31
(in thousands)	2016			2015
Deferred tax assets:
Net operating losses	$	34,902		$	31,464
Accruals		287			403
Deferred revenue		829			954
Stock options		1,894			1,558
Other deferred tax assets		765			652
Total deferred tax assets		38,677			35,031
Deferred tax liabilities:
Property and equipment		(32	)		(28	)
Total deferred tax liabilities		(32	)		(28	)
Valuation allowance		(38,645	)		(35,003	)
Net deferred taxes	$	—		$	—

Summary of Valuation Allowance [Table Text Block]

2016		2015		2014
$	3,642	$	8,101	$	6,286

Summary of Tax Credit Carryforwards [Table Text Block]

			Expiration
	Amount		Years
Net operating losses, federal	$	90,165	2024	-	2036
Net operating losses, state	$	78,219	2028	-	2036
Tax credits, federal	$	1,316	2031	-	2036
Tax credits, state	$	282	do not expire

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

	Year Ending December 31
(in thousands)	2016			2015			2014
Income tax provision (benefit) at federal statutory rate	$	(4,471	)	$	(6,439	)	$	(5,154	)
State tax		(157	)		(1,060	)		(818	)
ISO-related expense for GAAP		52			164			144
Change in valuation allowance		3,641			8,101			6,286
Revaluation of warrant liability		806			(731	)		(565	)
Tax credits		(31	)		(123	)		(44	)
Other		162			90			153
Total	$	2		$	2		$	2

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

	Year ended December 31,
(in thousands)	2016		2015
Unrecognized benefit - beginning of period	$	957	$	811
Gross increases - current period tax positions		17		76
Unrecognized benefit - end of period	$	974	$	957