Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Common Stock [Member]	Additional Paid-In Capital [Member]	Accumulated Deficit [Member]	Other Comprehensive Income (Loss) [Member]	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
Stock-based compensation		2,425			2,425
Other comprehensive income (loss)				(44)	(44)
Net loss			(17,019)		(17,019)
Balance, amount at Mar. 31, 2018	$ 5	420,294	(291,233)	(91)	128,975
Balance, shares at Mar. 31, 2018	47,603,568
Adoption of ASU No. 2014-09 on January 1, 2018 | ASU 2014-09			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 upon exercise of options		2			2
Issuance of common stock upon exercise of options, shares	770
Stock-based compensation		1,922			1,922
Other comprehensive income (loss)				50	50
Net loss			(26,144)		(26,144)
Balance, amount at Mar. 31, 2019	$ 6	$ 483,479	$ (391,656)	$ 12	$ 91,841
Balance, shares at Mar. 31, 2019	62,600,443

[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.