Condensed Statements of Changes in 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			$ 0		492				492
Issuance of common stock under employee stock purchase plan, shares			120,959
Issuance of common stock for services, amount					304				$ 304
Issuance of common stock for services, shares			75,183						75,183
Stock-based compensation					6,976				$ 6,976
Other comprehensive loss							30		30
Issuance of common stock, value	$ 1			$ 53,769				$ 53,770
Issuance of common stock, shares	14,375,000
Net loss						(63,436)			(63,436)
Balance, amount at Sep. 30, 2018			$ 6		479,109	(337,650)	(17)		141,448
Balance, shares at Sep. 30, 2018			62,106,121
Balance, amount at Jun. 30, 2018			$ 6		476,968	(313,524)	(36)		163,414
Balance, shares at Jun. 30, 2018			62,053,751
Issuance of common stock under employee stock purchase plan, amount					193				193
Issuance of common stock under employee stock purchase plan, shares			52,370
Issuance of common stock for services, amount									$ 300
Issuance of common stock for services, shares									0
Stock-based compensation					1,948				$ 1,948
Other comprehensive loss							19		19
Net loss						(24,126)			(24,126)
Balance, amount at Sep. 30, 2018			$ 6		479,109	(337,650)	(17)		141,448
Balance, shares at Sep. 30, 2018			62,106,121
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					397				397
Issuance of common stock under employee stock purchase plan, shares			160,744
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					21				$ 21
Issuance of common stock upon exercise of options, shares			6,964
Stock-based compensation					7,724				7,724
Other comprehensive loss							42		42
Issuance of common stock, shares		85,609
Net loss						(75,150)			(75,150)
Balance, amount at Sep. 30, 2019			$ 6		489,810	(440,662)	4		49,158
Balance, shares at Sep. 30, 2019			62,883,080
Balance, amount at Jun. 30, 2019			$ 6		485,718	(417,123)	16		68,617
Balance, shares at Jun. 30, 2019			62,800,869
Issuance of common stock under employee stock purchase plan, amount					200				200
Issuance of common stock under employee stock purchase plan, shares			77,698
Issuance of common stock for services, amount									$ 300
Issuance of common stock for services, shares									0
Issuance of common stock upon exercise of options					13				$ 13
Issuance of common stock upon exercise of options, shares			4,513
Stock-based compensation					3,879				3,879
Other comprehensive loss							(12)		(12)
Net loss						(23,539)			(23,539)
Balance, amount at Sep. 30, 2019			$ 6		$ 489,810	$ (440,662)	$ 4		$ 49,158
Balance, shares at Sep. 30, 2019			62,883,080

[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.