Note 12 - Equity-based Compensation (Tables)

12 Months Ended

Dec. 31, 2018

Notes Tables

Share-based Compensation, Stock Options, 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, 2015		388		$	32.03		6.2	$	19
Options granted		1,227		$	2.74
Restricted stock units granted		104		$	—
Options exercised		-		$	—
Restricted stock units vested		(114	)	$	—
Options forfeited/cancelled		(116	)	$	28.27
Restricted stock units cancelled		-		$	—
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
Vested and expected to vest at December 31, 2018		2,898		$	4.40		8.2	$	8
Vested at December 31, 2018		1,675		$	5.96		7.4	$	—
Exercisable at December 31, 2018		1,675		$	5.96		7.4	$	—

Schedule of Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Table Text Block]

	Year Ended December 31,
(in thousands)	2018		2017		2016
Research and development	$	32	$	113	$	195
Sales and Marketing		141		152		132
General and administrative		498		2,277		1,424
Total stock-based compensation expense	$	671	$	2,542	$	1,751

Nonemployees [Member]

Notes Tables

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

	Year Ended December 31,
Assumption	2018			2017			2016
Expected price volatility		85.03	%		87.41	%		87.68	%
Expected term (in years)		10.0			10.0			10.0
Risk-free interest rate		2.94	%		2.27	%		1.61	%
Dividend yield		0.00	%		0.00	%		0.00	%
Weighted-average fair value of options granted during the period	$	1.99		$	2.40		$	2.29

Employees and Directors [Member]

Notes Tables

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

	Year Ended December 31,
Assumption	2018			2017			2016
Expected price volatility		89.30	%		87.78	%		84.47	%
Expected term (in years)		5.98			6.90			7.03
Risk-free interest rate		2.80	%		2.12	%		1.57	%
Dividend yield		0.00	%		0.00	%		0.00	%
Weighted-average fair value of options granted during the period	$	1.51		$	2.34		$	2.06