STATEMENTS OF CHANGES IN STOCKHOLDERS’ EQUITY - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Accumulated Other Comprehensive Loss	Public Stock Offering	Public Stock Offering Common Stock	Public Stock Offering Additional Paid-In Capital	At-The-Market Offering	At-The-Market Offering Common Stock	At-The-Market Offering Additional Paid-In Capital	Registered Direct Offering	Registered Direct Offering Common Stock	Registered Direct Offering Additional Paid-In Capital
Beginning balance (in shares) at Dec. 31, 2017		1,973,039
Beginning balance at Dec. 31, 2017	$ 7,048	$ 0	$ 232,922	$ (225,874)	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock in connection with offering, net (in shares)		10,000,000
Issuance of common stock in connection with offering, net	45,604	$ 1	45,603
Issuance of common stock warrants in connection with build-to-suit obligation	243		243
Stock-based compensation	1,178		1,178
Unrealized gain (loss) on marketable securities	(5)				(5)
Net loss	$ (35,358)			(35,358)
Ending balance (in shares) at Dec. 31, 2018	11,973,039	11,973,039
Ending balance at Dec. 31, 2018	$ 18,710	$ 1	279,946	(261,232)	(5)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock in connection with offering, net (in shares)							5,750,000			3,599,141			2,181,034
Issuance of common stock in connection with offering, net						$ 18,331	$ 1	$ 18,330	$ 5,233		$ 5,233	$ 3,090		$ 3,090
Stock-based compensation	1,612		1,612
Unrealized gain (loss) on marketable securities	5				5
Net loss	$ (37,589)			(37,589)
Ending balance (in shares) at Dec. 31, 2019	23,503,214	23,503,214
Ending balance at Dec. 31, 2019	$ 9,392	$ 2	$ 308,211	$ (298,821)	$ 0