Note 2 - Summary of Significant Accounting Policies 1 (Tables)

9 Months Ended

12 Months Ended

Sep. 30, 2019

Dec. 31, 2018

Notes Tables

Schedule of Product Warranty Liability [Table Text Block]

Balance at December 31, 2018	$	272
Warranty provision		70
Usage/release		(128	)
Balance at September 30, 2019	$	214

	Year Ended December 31,
	2018			2017
Balance, beginning of year	$	390		$	509
Warranty provision		333			306
Usage/Release		(451	)		(425	)
Balance, end of year	$	272		$	390

Schedule of Earnings Per Share, Basic and Diluted [Table Text Block]

	Three Months Ended September 30,						Nine Months Ended September 30,
	2019			2018			2019			2018
Net loss attributable to common stockholders	$	(5,518	)	$	(6,224	)	$	(17,014	)	$	(28,766	)
Weighted average common stock outstanding		7,900			1,119			6,189			669
Net loss per share attributable to common stockholders, basic and diluted	$	(0.70	)	$	(5.56	)	$	(2.75	)	$	(43.00	)

	Year Ended December 31,
	2018			2017
Net loss attributable to common stockholders	$	(35,692	)	$	(48,732	)
Weighted average common stock outstanding		1,068			65
Net loss per share attributable to common stockholders, basic and diluted	$	(33.42	)	$	749.72	)

Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table Text Block]

	Three Months Ended September 30,				Nine Months Ended September 30,
	2019		2018		2019		2018
Common stock warrant equivalents		2,757,741		1,867,226		3,346,568		1,511,832
Common stock options		7,444		8,472		7,596		7,246
Convertible preferred stock		44,923		4,450		45,046		3,969
Unvested restricted stock units		371,651		84,848		316,575		374
		3,181,759		1,964,996		3,715,785		1,523,421

	Year Ended December 31,
	2018		2017
Common stock options		7,179		7,664
Convertible preferred stock		41,398		-
Unvested restricted stock units		92,245		508
Common stock warrants		2,077,871		5,371
		2,218,693		13,543