Condensed Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock [Member]	Common Stock Issuable [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Loss [Member]	Accumulated Deficit [Member]
Balance beginning at Dec. 31, 2017	$ 7,882	$ 202,156	$ 153	$ 40,522	$ (572)	$ (234,377)
Balance beginning (in shares) at Dec. 31, 2017		57,630,000	82,000
Issuance of shares of common stock, net of issuance costs	3,992	$ 3,992
Issuance of shares of common stock, net of issuance costs (in shares)		2,224,000
Warrants exercise	7	$ 7
Warrants exercise (in shares)		5,000
Common stock issuance for services	65		$ 65
Common stock issuance for services (in shares)			34,000
Release of restricted stock units (in shares)		12,000
Stock-based compensation expense	1,285			1,285
Exercise of common stock options	8	$ 8
Exercise of common stock options (in shares)		5,000
Net loss	(9,753)					(9,753)
Foreign currency translation adjustment	45				45
Balance ending at Mar. 31, 2018	3,531	$ 206,163	$ 218	41,807	(527)	(244,130)
Balance ending (in shares) at Mar. 31, 2018		59,876,000	116,000
Balance beginning at Dec. 31, 2017	7,882	$ 202,156	$ 153	40,522	(572)	(234,377)
Balance beginning (in shares) at Dec. 31, 2017		57,630,000	82,000
Net loss	(26,236)
Foreign currency translation adjustment	(8)
Balance ending at Sep. 30, 2018	3,892	$ 221,774		43,311	(580)	(260,613)
Balance ending (in shares) at Sep. 30, 2018		70,312,000
Balance beginning at Mar. 31, 2018	3,531	$ 206,163	$ 218	41,807	(527)	(244,130)
Balance beginning (in shares) at Mar. 31, 2018		59,876,000	116,000
Issuance of shares of common stock, net of issuance costs	9,978	$ 9,978
Issuance of shares of common stock, net of issuance costs (in shares)		6,757,000
Issuance of common stock inconnection with employeestock purchase plan	261	$ 261
Issuance of shares of common stock in connection with employee stock purchase plan (in shares)		226,000
Common stock issuance for services	44	$ 262	$ (218)
Common stock issuance for services (in shares)		133,000	(116,000)
Release of restricted stock units (in shares)		12,000
Stock-based compensation expense	627			627
Exercise of common stock options	141	$ 141
Exercise of common stock options (in shares)		71,000
Net loss	(7,961)					(7,961)
Foreign currency translation adjustment	(77)				(77)
Balance ending at Jun. 30, 2018	6,544	$ 216,805		42,434	(604)	(252,091)
Balance ending (in shares) at Jun. 30, 2018		67,075,000
Issuance of shares of common stock, net of issuance costs	4,969	$ 4,969
Issuance of shares of common stock, net of issuance costs (in shares)		3,225,000
Release of restricted stock units (in shares)		12,000
Stock-based compensation expense	877			877
Net loss	(8,522)					(8,522)
Foreign currency translation adjustment	24				24
Balance ending at Sep. 30, 2018	3,892	$ 221,774		43,311	(580)	(260,613)
Balance ending (in shares) at Sep. 30, 2018		70,312,000
Balance beginning at Dec. 31, 2018	$ 3,084	$ 229,019		44,111	(575)	(269,471)
Balance beginning (in shares) at Dec. 31, 2018	76,336,000	76,336,000
Adoption of ASC Topic 842-Leases (see note 2) at Dec. 31, 2018	$ (144)					(144)
Issuance of shares of common stock andwarrants in connection with rights offering,net of issuance costs	34,399	$ 34,399
Issuance of shares of common stock and warrants in connection with rights offering, net of issuance costs (in shares)		47,812,000
Release of restricted stock units (in shares)		50,000
Warrants modification (see note 7)				1,577		(1,577)
Stock-based compensation expense	898			898
Net loss	(9,700)					(9,700)
Foreign currency translation adjustment	(8)				(8)
Balance ending at Mar. 31, 2019	28,529	$ 263,418		46,586	(583)	(280,892)
Balance ending (in shares) at Mar. 31, 2019		124,198,000
Balance beginning at Dec. 31, 2018	$ 3,084	$ 229,019		44,111	(575)	(269,471)
Balance beginning (in shares) at Dec. 31, 2018	76,336,000	76,336,000
Adoption of ASC Topic 842-Leases (see note 2) at Dec. 31, 2018	$ (144)					(144)
Net loss	(25,724)
Foreign currency translation adjustment	(10)
Balance ending at Sep. 30, 2019	$ 14,286	$ 263,656		48,131	(585)	(296,916)
Balance ending (in shares) at Sep. 30, 2019	124,598,000	124,598,000
Balance beginning at Mar. 31, 2019	$ 28,529	$ 263,418		46,586	(583)	(280,892)
Balance beginning (in shares) at Mar. 31, 2019		124,198,000
Issuance of common stock inconnection with employeestock purchase plan	238	$ 238
Issuance of shares of common stock in connection with employee stock purchase plan (in shares)		376,000
Release of restricted stock units (in shares)		12,000
Stock-based compensation expense	859			859
Net loss	(8,440)					(8,440)
Foreign currency translation adjustment	9				9
Balance ending at Jun. 30, 2019	21,195	$ 263,656		47,445	(574)	(289,332)
Balance ending (in shares) at Jun. 30, 2019		124,586,000
Release of restricted stock units (in shares)		12,000
Stock-based compensation expense	686			686
Net loss	(7,584)					(7,584)
Foreign currency translation adjustment	(11)				(11)
Balance ending at Sep. 30, 2019	$ 14,286	$ 263,656		$ 48,131	$ (585)	$ (296,916)
Balance ending (in shares) at Sep. 30, 2019	124,598,000	124,598,000