Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Common Stock Issuable [Member]	Additional Paid-in Capital [Member]	Notes Receivable for Stock Option Exercises [Member]	Accumulated Other Comprehensive Loss [Member]	Accumulated Deficit [Member]
Balance beginning at Dec. 31, 2015	$ 20,263	$ 166,049	$ 205	$ 27,277	$ (5)	$ (581)	$ (172,682)
Balance beginning (in shares) at Dec. 31, 2015		35,942,000	33,000
Issuance of common stock and options in connection with rights offering, net of issuance costs	19,483	$ 19,430		53
Issuance of common stock and options in connection with rights offering net of issuance costs (in shares)		5,978,000
Issuance of shares under Long-Term Investor Right (in shares)		355,000
Issuance of common stock in connection with employee stock purchase plan	488	$ 488
Issuance of common stock in connection with Employee Stock Purchase Plan (in shares)		189,000
Exercise of stock options	481	$ 478			3
Exercise of stock options (in shares)		96,000
Stock-based compensation expense	3,367			3,367
Common stock issuance for services	$ 272	$ 324	$ (52)
Common stock issuance for services (in shares)	82,000	82,000	44,000
Release of restricted stock units (in shares)		59,000
Comprehensive loss:
Net loss	$ (33,179)						(33,179)
Foreign currency translation adjustments	(27)					(27)
Comprehensive loss	(33,206)					(27)	(33,179)
Balance ending at Dec. 31, 2016	11,148	$ 186,769	$ 153	30,697	(2)	(608)	(205,861)
Balance ending (in shares) at Dec. 31, 2016		42,701,000	77,000
Issuance of common stock and options in connection with rights offering, net of issuance costs	19,668	$ 13,647		6,021
Issuance of common stock and options in connection with rights offering net of issuance costs (in shares)		13,653,000
Issuance of common stock, net of issuance costs	1,084	$ 1,084
Issuance of shares common stock, net of issuance costs (in shares)		598,000
Issuance of common stock in connection with employee stock purchase plan	394	$ 394
Issuance of common stock in connection with Employee Stock Purchase Plan (in shares)		407,000
Repayment of notes receivable for stock option exercises, net	2				$ 2
Stock-based compensation expense	3,784			3,784
Fair value of stock options issuedfor services	20			20
Common stock issuance for services	$ 262	$ 262
Common stock issuance for services (in shares)	223,000	223,000	5,000
Release of restricted stock units (in shares)		48,000
Comprehensive loss:
Net loss	$ (28,516)						(28,516)
Foreign currency translation adjustments	36					36
Comprehensive loss	(28,480)					36	(28,516)
Balance ending at Dec. 31, 2017	$ 7,882	$ 202,156	$ 153	40,522		(572)	(234,377)
Balance ending (in shares) at Dec. 31, 2017	57,630,000	57,630,000	82,000
Issuance of common stock, net of issuance costs	$ 25,936	$ 25,936
Issuance of shares common stock, net of issuance costs (in shares)		17,949,000
Issuance of common stock in connection with employee stock purchase plan	508	$ 508
Issuance of common stock in connection with Employee Stock Purchase Plan (in shares)		494,000
Exercise of stock options	149	$ 149
Exercise of stock options (in shares)		76,000
Stock-based compensation expense	3,589			3,589
Issuance of common stock in connection with warrant exercise	8	$ 8
Issuance of common stock in connection with warrant exercise (in shares)		6,000
Common stock issuance for services	109	$ 262	$ (153)
Common stock issuance for services (in shares)		132,996	(82,000)
Release of restricted stock units (in shares)		48,000
Comprehensive loss:
Net loss	(35,094)						(35,094)
Foreign currency translation adjustments	(3)					(3)
Comprehensive loss	(35,097)					(3)	(35,094)
Balance ending at Dec. 31, 2018	$ 3,084	$ 229,019		$ 44,111		$ (575)	$ (269,471)
Balance ending (in shares) at Dec. 31, 2018	76,336,000	76,336,000