Statements of Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Common stock	Additional paid-in capital	Accumulated other comprehensive income (loss)	Accumulated deficit	Convertible Preferred Stock
Beginning balance (in shares) at Dec. 31, 2017		8,662,435
Beginning balance at Dec. 31, 2017	$ 35,216	$ 9	$ 381,199	$ (134)	$ (345,858)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of options (in shares)		328
Issuance of common stock upon exercise of options	1		1
Issuance of common stock upon vesting of restricted stock units (in shares)		128,840
Stock-based compensation expense	5,441		5,441
Issuance of common stock under Employee Stock Purchase Plan (in shares)		26,416
Issuance of common stock under Employee Stock Purchase Plan	219		219
Unrealized gain on short-term investments	134			134
Net loss	(48,709)				(48,709)
Ending balance (in shares) at Dec. 31, 2018		8,818,019
Ending balance at Dec. 31, 2018	(5,854)	$ 9	386,860	0	(392,723)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of options (in shares)		2,750
Issuance of common stock upon exercise of options	3		3
Issuance of common stock upon vesting of restricted stock units (in shares)		559,445
Stock-based compensation expense	2,288		2,288
Issuance of common stock, preferred stock and warrants from private placement, net of offering costs (in shares)		9,730,534				3,704,288
Issuance of common stock, preferred stock and warrants from private placement, net of offering costs	40,084	$ 10	40,070			$ 4
Issuance of common stock under Employee Stock Purchase Plan (in shares)		4,035
Issuance of common stock under Employee Stock Purchase Plan	3		3
Issuance of common stock, net of $292 of offering costs (in shares)		1,903,880
Issuance of common stock through ATM	2,083	$ 2	2,081
Net loss	(18,592)				(18,592)
Ending balance (in shares) at Dec. 31, 2019		21,018,663				3,704,288
Ending balance at Dec. 31, 2019	$ 20,015	$ 21	$ 431,305	$ 0	$ (411,315)	$ 4