Unaudited Condensed Statement of Changes in Stockholders' Deficit - USD ($) $ in Thousands	Purchase Agreement [Member] Series A Convertible Preferred Stock [Member]	Purchase Agreement [Member] Undesignated Preferred Stock [Member]	Purchase Agreement [Member] Common Stock [Member]	Purchase Agreement [Member] Additional Paid-in Capital [Member]	Purchase Agreement [Member] Retained Earnings [Member]	Purchase Agreement [Member]	Series A Convertible Preferred Stock [Member]	Undesignated Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Total
Balance at Dec. 31, 2017									$ 1	$ 107,209	$ (164,726)	$ (57,516)
Net loss											(26,219)	(26,219)
Stock-based compensation expense										1,281		1,281
Issuance of common stock in connection with ATM, net of commissions			$ 1	$ 2,797		$ 2,798
Offering expenses charged to equity										(27)		(27)
Balance at Mar. 31, 2018									2	111,260	(190,945)	(79,683)
Balance at Dec. 31, 2018									3	154,623	(221,192)	(66,566)
Net loss											(12,291)	(12,291)
Stock-based compensation expense										1,290		1,290
Issuance of common stock in connection with ATM, net of commissions				$ 2,721		$ 2,721
Offering expenses charged to equity										10		10
Balance at Mar. 31, 2019									$ 3	$ 158,644	$ (233,483)	$ (74,836)