Consolidated Statements of Stockholders' Equity (Deficiency) - USD ($) $ in Thousands	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]	Total
Balance beginning at Dec. 31, 2013	$ 88,311		$ 20,785	$ (587)	$ (267)	$ (117,463)	$ (9,221)
Balance beginning (in shares) at Dec. 31, 2013	23,050
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options	$ 506						506
Exercise of stock options (in shares)	115
Stock-based compensation expense			1,475				1,475
Stock issued in connection with professional services	$ 178						178
Stock issued in connection with professional services (in shares)	22
Issuance of common stock in connection with warrant exercise	$ 10						10
Issuance of common stock in connection with warrant exercise (in shares)	2
Issuance of common stock in connection with private placement	$ 9,099						9,099
Issuance of common stock in connection with private placement (in shares)	1,300
Issuance of common stock in connection with initial public offering	$ 36,225						36,225
Issuance of common stock in connection with initial public offering (in shares)	4,025
Issuance costs of initial public offering	$ (4,971)						(4,971)
Fair value of warrants issued in connection with initial public offering			2,772				2,772
Issuance of common stock in connection with conversion of convertible promissory notes	$ 33,196						33,196
Issuance of common stock in connection with conversion of convertible promissory notes (in shares)	6,639
Finders' fee paid on private placement	$ 451		(451)
Finders' fee paid on private placement (in shares)	64
Common stock cancelled	$ (9)		9
Common stock cancelled (in shares)	(1)
Common stock issuable for services		$ 166					166
Common stock issuable for services (in shares)		16
Stock grant in connection with services by a director	$ 175						175
Stock grant in connection with services by a director (in shares)	25
Repayment of notes receivable for stock option exercises, net				(7)			(7)
Forgiveness of notes receivable from an officer for stock option exercises				423			423
Comprehensive loss:
Net loss						(35,201)	(35,201)
Foreign currency translation adjustment					(207)		(207)
Comprehensive loss					(207)	(35,201)	(35,408)
Balance ending at Dec. 31, 2014	$ 163,171	$ 166	24,590	(171)	(474)	(152,664)	34,618
Balance ending (in shares) at Dec. 31, 2014	35,241	16
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock in connection with Employee Stock Purchase Plan	$ 226						226
Issuance of common stock in connection with Employee Stock Purchase Plan (in shares)	53
Exercise of stock options	$ 2,782						2,782
Exercise of stock options (in shares)	574
Stock-based compensation expense			2,687				2,687
Stock issued in connection with professional services	$ 285	$ 39					$ 324
Stock issued in connection with professional services (in shares)	23	17					23,136
Issuance of common stock in connection with warrant exercise	$ 702						$ 702
Issuance of common stock in connection with warrant exercise (in shares)	140
Common stock issuable for services							285
Stock grant in connection with services by a director
Repayment of notes receivable for stock option exercises, net				166			166
Issuance of common stock in connection with cashless exercise of warrants
Issuance of common stock in connection with cashless exercise of warrants (in shares)	1
Common stock tendered to exercise stock options	$ (993)						(993)
Common stock tendered to exercise stock options (in shares)	(78)
Common stock tendered to pay taxes on stock option exercise	$ (124)						(124)
Common stock tendered to pay taxes on stock option exercise (in shares)	(12)
Comprehensive loss:
Net loss						(20,018)	(20,018)
Foreign currency translation adjustment					(107)		(107)
Comprehensive loss					(107)	(20,018)	(20,125)
Balance ending at Dec. 31, 2015	$ 166,049	$ 205	27,277	(5)	(581)	(172,682)	20,263
Balance ending (in shares) at Dec. 31, 2015	35,942	33
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock and options in connection with rights offering net of expenses	$ 19,430		53				19,483
Issuance of common stock and options in connection with rights offering net of expenses (in shares)	5,978
Issuance of shares under Long-Term Investor Right
Issuance of shares under Long-Term Investor Right (in shares)	355
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
Exercise of stock options	$ 478			3			481
Exercise of stock options (in shares)	96
Stock-based compensation expense			3,367				3,367
Stock issued in connection with professional services	$ 324	$ (52)					$ 272
Stock issued in connection with professional services (in shares)	82	44					82,000
Issuance of RSU units
Issuance of RSU units (in shares)	59
Common stock issuable for services							324
Stock grant in connection with services by a director
Comprehensive loss:
Net loss						(33,179)	(33,179)
Foreign currency translation adjustment					(27)		(27)
Comprehensive loss					(27)	(33,179)	(33,206)
Balance ending at Dec. 31, 2016	$ 186,769	$ 153	$ 30,697	$ (2)	$ (608)	$ (205,861)	$ 11,148
Balance ending (in shares) at Dec. 31, 2016	42,701	77