Consolidated statements of stockholders equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Loss [Member]
Beginning balance at Dec. 31, 2014	$ 36,147		$ 125,567	$ (89,416)	$ (4)
Beginning balance, shares at Dec. 31, 2014		10,695,108
Issuance of common stock, net share issuance costs	91,793		91,793
Issuance of common stock, net share issuance costs, shares		6,325,000
Options exercised	1,120		1,120
Options exercised, shares		191,878
Stock-based compensation	1,506		1,506
Other comprehensive income (loss)	(286)				(286)
Net loss	(21,860)			(21,860)
Ending balance at Dec. 31, 2015	108,420		219,986	(111,276)	(290)
Ending balance, shares at Dec. 31, 2015		17,211,986
Issuance of common stock, net share issuance costs	70,676		70,676
Issuance of common stock, net share issuance costs, shares		6,152,500
Options exercised	440		440
Options exercised, shares		55,663
Exercise of warrants	43		43
Exercise of warrants, shares		3,001
Stock-based compensation	1,966		1,966
Other comprehensive income (loss)	121				121
Net loss	(37,002)			(37,002)
Ending balance at Dec. 31, 2016	$ 144,664		293,111	(148,278)	(169)
Ending balance, shares at Dec. 31, 2016	23,423,150	23,423,150
Cumulative effect of adoption of new accounting standard (Note 2(p)) at Dec. 31, 2016			41	(41)
Beginning balance at Dec. 31, 2016	$ 144,664		293,152	(148,319)	(169)
Options exercised	$ 468		468
Options exercised, shares	49,280	49,280
Stock-based compensation	$ 3,839		3,839
Other comprehensive income (loss)	99				99
Net loss	(50,183)			(50,183)
Ending balance at Dec. 31, 2017	$ 98,887		$ 297,459	$ (198,502)	$ (70)
Ending balance, shares at Dec. 31, 2017	23,472,430	23,472,430