Note 13 - Equity-based Compensation (Tables)

12 Months Ended

Dec. 31, 2019

Notes Tables

Share-based Payment Arrangement, Option, Activity [Table Text Block]

(in thousands, except years and per share data)	Options			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Life (years)		Aggregate Intrinsic Value
Outstanding at December 31, 2016		1,489		$	8.38		8.7	$	702
Options granted		1,616		$	3.03
Restricted stock units granted		49		$	—
Options exercised		(68	)	$	2.72
Restricted stock units vested		(39	)	$	—
Options forfeited/cancelled		(87	)	$	22.08
Restricted stock units cancelled		-		$	—
Outstanding at December 31, 2017		2,960		$	5.16		8.6	$	2,586
Options granted		1,118		$	2.03
Restricted stock units granted		12		$	—
Options exercised		(4	)	$	2.35
Restricted stock units vested		-		$	—
Options forfeited/cancelled		(701	)	$	5.12
Restricted stock units cancelled		(11	)	$	—
Outstanding at December 31, 2018		3,374		$	4.13		8.2	$	8
Options granted		145		$	0.37
Restricted stock units granted		204		$	—
Options exercised		(83	)	$	2.30
Restricted stock units vested		(209	)	$	—
Options forfeited/cancelled		(1,247	)	$	4.01
Restricted stock units cancelled		(1	)	$	—
Outstanding at December 31, 2019		2,183		$	4.03		6.6	$	43
Vested and expected to vest at December 31, 2019		2,165		$	4.05		6.5	$	43
Vested at December 31, 2019		1,818		$	4.44		6.2	$	—
Exercisable at December 31, 2019		1,818		$	4.44		6.2	$	—

Share-based Payment Arrangement, Expensed and Capitalized, Amount [Table Text Block]

	Year Ended December 31,
(in thousands)	2019		2018		2017
Research and development	$	42	$	32	$	113
Sales and marketing		93		141		152
General and administrative		351		498		2,277
Total stock-based compensation expense	$	486	$	671	$	2,542

Nonemployees [Member]

Notes Tables

Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]

	Year Ended December 31,
Assumption	2018			2017
Expected price volatility		85.03	%		87.41	%
Expected term (in years)		10.0			10.0
Risk-free interest rate		2.94	%		2.27	%
Dividend yield		0.00	%		0.00	%
Weighted-average fair value of options granted during the period	$	1.99		$	2.40

Employees and Directors [Member]

Notes Tables

Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]

	Year Ended December 31,
Assumption	2019			2018			2017
Expected price volatility		112.41	%		89.30	%		87.78	%
Expected term (in years)		6.14			5.98			6.90
Risk-free interest rate		1.99	%		2.80	%		2.12	%
Dividend yield		0.00	%		0.00	%		0.00	%
Weighted-average fair value of options granted during the period	$	0.31		$	1.51		$	2.34