Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Common Stock [Member] Underwriters' option	Common Stock [Member] Restricted Stock Units (RSUs) [Member]	Common Stock [Member]	Additional Paid-In Capital [Member] Underwriters' option	Additional Paid-In Capital [Member]	Accumulated Deficit [Member]	Other Comprehensive Income (Loss) [Member]	Underwriters' option	Total
Balance, amount at Dec. 31, 2017			$ 5		$ 417,568	$ (278,214)	$ (47)		$ 139,312
Balance, shares at Dec. 31, 2017			47,534,979
Issuance of common stock under employee stock purchase plan, amount					301				301
Issuance of common stock under employee stock purchase plan, shares			68,589
Issuance of common stock for services, amount					302				$ 302
Issuance of common stock for services, shares			75,183						75,183
Stock-based compensation					5,028				$ 5,028
Other comprehensive income							11		11
Issuance of common stock, value	$ 1			$ 53,769				$ 53,770
Issuance of common stock, shares	14,375,000
Net loss						(39,310)			(39,310)
Balance, amount at Jun. 30, 2018			$ 6		476,968	(313,524)	(36)		163,414
Balance, shares at Jun. 30, 2018			62,053,751
Balance, amount at Mar. 31, 2018			$ 5		420,294	(291,233)	(91)		128,975
Balance, shares at Mar. 31, 2018			47,603,568
Issuance of common stock for services, amount					302				$ 302
Issuance of common stock for services, shares			75,183						75,183
Stock-based compensation					2,603				$ 2,603
Other comprehensive income							55		55
Issuance of common stock, value	$ 1			$ 53,769				$ 53,770
Issuance of common stock, shares	14,375,000
Net loss						(22,291)			(22,291)
Balance, amount at Jun. 30, 2018			$ 6		476,968	(313,524)	(36)		163,414
Balance, shares at Jun. 30, 2018			62,053,751
Adoption of ASU No. 2014-09 on January 1, 2018						4,000			4,000
Balance, amount at Dec. 31, 2018			$ 6		481,357	(365,512)	(38)		115,813	[1]
Balance, shares at Dec. 31, 2018			62,516,627
Issuance of common stock under employee stock purchase plan, amount					198				198
Issuance of common stock under employee stock purchase plan, shares			83,046
Issuance of common stock for services, amount					311				$ 311
Issuance of common stock for services, shares			113,136						113,136
Issuance of common stock upon exercise of options					7				$ 7
Issuance of common stock upon exercise of options, shares			2,451
Stock-based compensation					3,845				3,845
Other comprehensive income							54		54
Issuance of common stock, shares		85,609
Net loss						(51,611)			(51,611)
Balance, amount at Jun. 30, 2019			$ 6		485,718	(417,123)	16		68,617
Balance, shares at Jun. 30, 2019			62,800,869
Balance, amount at Mar. 31, 2019			$ 6		483,479	(391,656)	12		91,841
Balance, shares at Mar. 31, 2019			62,600,443
Issuance of common stock for services, amount					311				$ 311
Issuance of common stock for services, shares			113,136						113,136
Issuance of common stock upon exercise of options					5				$ 5
Issuance of common stock upon exercise of options, shares			1,681
Stock-based compensation					1,923				1,923
Other comprehensive income							4		4
Issuance of common stock, shares		85,609
Net loss						(25,467)			(25,467)
Balance, amount at Jun. 30, 2019			$ 6		$ 485,718	$ (417,123)	$ 16		$ 68,617
Balance, shares at Jun. 30, 2019			62,800,869

[1] Derived from the audited consolidated financial statements included in the Company’s Annual Report on Form 10K for the year ended December 31, 2018.