Note 14 - Income Taxes (Tables)

12 Months Ended

Dec. 31, 2018

Notes Tables

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

	Years ended December 31,
	2018			2017			2016
Tax at federal statutory rate	$	(2,937	)	$	(4,185	)	$	(3,505	)
State, net of federal benefit		(455	)		(1,238	)		(315	)
Research and development credit		(236	)		(135	)		(89	)
Stock-based compensation		440			344			136
Nondeductible interest		—			—			590
Warrant and derivative revaluation		—			—			328
Change in Federal tax rate		—			8,172			—
Other		22			7			94
Change in valuation allowance		3,166			(2,965	)		2,761
Total provision for income taxes	$	—		$	—		$	—

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

	December 31,
	2018			2017
Accrued compensation	$	84		$	110
Inventory adjustments		276			449
Depreciation and amortization - noncurrent		113			146
Share-based compensation		648			558
Net operating loss and tax credit carryforwards - noncurrent		20,698			17,368
Other		12			34
Gross deferred tax asset		21,831			18,665
Valuation allowance		(21,831	)		(18,665	)
Net deferred tax asset	$	—		$	—

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

	December 31,
	2018		2017
Balance, beginning of year	$	725	$	608
Additions based on tax positions related to the current year		166		117
Additions (reductions) for tax positions related to prior years		—		—
Balance, end of year	$	891	$	725