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, 2015	$ 108,420		$ 219,986	$ (111,276)	$ (290)
Beginning 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	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
Cumulative effect of adoption of new accounting standard 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
Stock-based compensation	3,839		3,839
Other comprehensive income	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
Options exercised	$ 602		602
Options exercised, shares	64,938	64,938
Stock-based compensation	$ 4,698		4,698
Other comprehensive income	70				$ 70
Net loss	(31,585)			(31,585)
Ending balance at Dec. 31, 2018	$ 72,672		$ 302,759	$ (230,087)
Ending balance, shares at Dec. 31, 2018	23,537,368	23,537,368