CONSOLIDATED STATEMENTS OF CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS' EQUITY (DEFICIT) - USD ($) $ in Thousands	Total	Initial Public Offering	Follow On Offering	ATM	Convertible Preferred Stock	Common Stock	Common Stock Initial Public Offering	Common Stock Follow On Offering	Common Stock ATM	Additional Paid-in Capital	Additional Paid-in Capital Initial Public Offering	Additional Paid-in Capital Follow On Offering	Additional Paid-in Capital ATM	Accumulated Other Comprehensive Gain (Loss)	Accumulated Deficit
Balance balance at Dec. 31, 2017					$ 137,762
Beginning balance at Dec. 31, 2017	$ (39,454)									$ 800				$ (73)	$ (40,181)
Beginning balance, Shares at Dec. 31, 2017					127,199,705
Beginning balance, Shares at Dec. 31, 2017						2,637,011
Conversion of convertible preferred stock into common stock upon initial public offering	137,762				$ (137,762)	$ 2				137,760
Conversion of convertible preferred stock into common stock upon initial public offering, Shares					(127,199,705)
Conversion of convertible preferred stock into common stock upon initial public offering, Shares						24,168,656
Issuance of common stock, net of discounts and issuance costs		$ 150,843					$ 1				$ 150,842
Issuance of common stock, net of discounts and issuance costs, Shares							10,350,000
Vesting of common stock from option exercises	75									75
Vesting of common stock from option exercises, Shares						129,959
Issuance of common stock from option exercises	87									87
Issuance of common stock from option exercises, Shares						72,900
Stock-based compensation	2,623									2,623
Other comprehensive gain (loss)	(4)													(4)
Net loss	(55,577)														(55,577)
Ending balance at Dec. 31, 2018	196,355					$ 3				292,187				(77)	(95,758)
Ending balance, Shares at Dec. 31, 2018						37,358,526
Issuance of common stock, net of discounts and issuance costs			$ 134,524	$ 22,409				$ 1				$ 134,523	$ 22,409
Issuance of common stock, net of discounts and issuance costs, Shares				1,105,000				6,388,889	1,105,000
Issuance of common stock pursuant to employee stock purchase plan	829									829
Issuance of common stock pursuant to employee stock purchase plan, Shares						55,234
Vesting of common stock from option exercises	60									60
Vesting of common stock from option exercises, Shares						94,816
Issuance of common stock from option exercises	$ 351									351
Issuance of common stock from option exercises, Shares	114,277					114,277
Stock-based compensation	$ 7,635									7,635
Other comprehensive gain (loss)	260													260
Net loss	(103,916)														(103,916)
Ending balance at Dec. 31, 2019	$ 258,507					$ 4				$ 457,994				$ 183	$ (199,674)
Ending balance, Shares at Dec. 31, 2019						45,116,742