CONDENSED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY (DEFICIT) - USD ($) $ in Thousands	Total	Common stock	Additional paid-in capital	Accumulated deficit	Convertible preferred stock	ATM	ATM Common stock	ATM Additional paid-in capital	Preferred Stock and Warrants from Private Placement	Preferred Stock and Warrants from Private Placement Common stock	Preferred Stock and Warrants from Private Placement Additional paid-in capital
Beginning balance (in shares) at Dec. 31, 2018		8,818,019			0
Beginning balance at Dec. 31, 2018	$ (5,854)	$ 9	$ 386,860	$ (392,723)	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon vesting of restricted stock units (in shares)		93,648
Issuance of new shares (in shares)							1,903,880
Issuance of new shares						$ 2,084	$ 2	$ 2,082
Issuance of common stock under Employee Stock Purchase Plan (in shares)		2,369
Issuance of common stock under Employee Stock Purchase Plan	2		2
Stock-based compensation expense	959		959
Net loss	(3,260)			(3,260)
Ending balance (in shares) at Mar. 31, 2019		10,817,916			0
Ending balance at Mar. 31, 2019	(6,069)	$ 11	389,903	(395,983)	$ 0
Beginning balance (in shares) at Dec. 31, 2018		8,818,019			0
Beginning balance at Dec. 31, 2018	(5,854)	$ 9	386,860	(392,723)	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(8,276)
Ending balance (in shares) at Jun. 30, 2019		20,824,388			415,898
Ending balance at Jun. 30, 2019	4,743	$ 21	405,721	(400,999)	$ 0
Beginning balance (in shares) at Mar. 31, 2019		10,817,916			0
Beginning balance at Mar. 31, 2019	(6,069)	$ 11	389,903	(395,983)	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon vesting of restricted stock units (in shares)		273,438
Issuance of common stock upon exercise of options (in shares)		2,500
Issuance of common stock upon exercise of stock options	2		2
Issuance of new shares (in shares)									415,898	9,730,534
Issuance of new shares									$ 15,505	$ 10	$ 15,495
Stock-based compensation expense	321		321
Net loss	(5,016)			(5,016)
Ending balance (in shares) at Jun. 30, 2019		20,824,388			415,898
Ending balance at Jun. 30, 2019	4,743	$ 21	405,721	(400,999)	$ 0
Beginning balance (in shares) at Dec. 31, 2019		21,018,663			3,704,288
Beginning balance at Dec. 31, 2019	20,015	$ 21	431,305	(411,315)	$ 4
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon vesting of restricted stock units (in shares)		21,166
Issuance of common stock upon exercise of options (in shares)		468
Issuance of common stock under Employee Stock Purchase Plan (in shares)		1,666
Issuance of common stock under Employee Stock Purchase Plan	1		1
Conversions of convertible preferred stock (in shares)		6,566,820			(656,682)
Conversions of convertible preferred stock		$ 7	(6)		$ (1)
Stock-based compensation expense	823		823
Net loss	(5,937)			(5,937)
Ending balance (in shares) at Mar. 31, 2020		27,608,783			3,047,606
Ending balance at Mar. 31, 2020	14,902	$ 28	432,123	(417,252)	$ 3
Beginning balance (in shares) at Dec. 31, 2019		21,018,663			3,704,288
Beginning balance at Dec. 31, 2019	20,015	$ 21	431,305	(411,315)	$ 4
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(12,884)
Ending balance (in shares) at Jun. 30, 2020		35,922,916			2,217,963
Ending balance at Jun. 30, 2020	8,584	$ 36	432,745	(424,199)	$ 2
Beginning balance (in shares) at Mar. 31, 2020		27,608,783			3,047,606
Beginning balance at Mar. 31, 2020	14,902	$ 28	432,123	(417,252)	$ 3
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon vesting of restricted stock units (in shares)		17,703
Conversions of convertible preferred stock (in shares)		8,296,430			(829,643)
Conversions of convertible preferred stock		$ 8	(7)		$ (1)
Stock-based compensation expense	629		629
Net loss	(6,947)			(6,947)
Ending balance (in shares) at Jun. 30, 2020		35,922,916			2,217,963
Ending balance at Jun. 30, 2020	$ 8,584	$ 36	$ 432,745	$ (424,199)	$ 2