Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity - USD ($) $ in Thousands	Total	Series G redeemable convertible preferred stock	Series H redeemable convertible preferred stock	Common Stock	Additional Paid-In Capital	Accumulated Deficit
Beginning balance (in shares) at Dec. 31, 2018	532,606,084
Beginning balance at Dec. 31, 2018	$ 105,232
Increase (Decrease) in Temporary Equity [Roll Forward]
Accretion of redeemable convertible preferred stock	4,640
Issuance of Series redeemable convertible preferred stock for aggregate proceeds, net of issuance costs (in shares)		148,928,337	233,446,519
Issuance of Series redeemable convertible preferred stock for aggregate proceeds, net of issuance costs		$ 11,492	$ 3,941
Deemed dividend recognized on beneficial conversion features of Series H redeemable convertible preferred stock (Note 7)	$ 6,741		6,741
Deemed dividend from conversion of Series G to Series H redeemable convertible preferred stock (Note 7) (in shares)	97,592,739
Deemed dividend from conversion of Series G to Series H redeemable convertible preferred stock (Note 7)	$ 6,860
Conversion of preferred stock to common stock in connection with initial public offering (in shares)	(1,012,573,679)
Conversion of preferred stock to common stock in connection with initial public offering (Note 7)	$ (138,906)
Ending balance (in shares) at Dec. 31, 2019	0
Ending balance at Dec. 31, 2019	$ 0
Beginning balance (in shares) at Dec. 31, 2018				63,005
Beginning balance at Dec. 31, 2018	(111,966)			$ 0	$ 40,598	$ (152,564)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Accretion of redeemable convertible preferred stock	(4,640)				(4,640)
Exercise of stock options (in shares)				1,548
Exercise of stock options	4				4
Stock-based compensation	572				572
Issuance of Series H redeemable convertible preferred stock for aggregate proceeds of $0.047 per share, net of issuance costs of $318 (Note 7)	6,741				6,741
Deemed dividend recognized on beneficial conversion features of Series H redeemable convertible preferred stock (Note 7)	(6,741)				(6,741)
Deemed dividend from conversion of Series G to Series H redeemable convertible preferred stock (Note 7)	(6,860)				(6,860)
Conversion of preferred stock to common stock in connection with initial public offering (Noted 7) (in shares)				7,816,643
Conversion of preferred stock to common stock in connection with initial public offering (Note 7)	138,906			$ 8	138,898
Issuance of common stock in initial public offering, net of underwriting discount, commissions and issuance costs (Note 8) (in shares)				4,140,000
Issuance of common stock in initial public offering, net of underwriting discount, commissions and issuance costs (Note 8)	50,444			$ 4	50,440
Net exercise of common and preferred stock warrants (in shares)				539,794
Net exercise of common and preferred stock warrants	511			$ 1	510
Reclassification of redeemable convertible preferred stock warrant liabilities as equity	726				726
Net loss	$ (12,038)					(12,038)
Ending balance (in shares) at Dec. 31, 2019	12,560,990			12,560,990
Ending balance at Dec. 31, 2019	$ 55,659			$ 13	220,248	(164,602)
Increase (Decrease) in Temporary Equity [Roll Forward]
Accretion of redeemable convertible preferred stock	$ 0
Deemed dividend recognized on beneficial conversion features of Series H redeemable convertible preferred stock (Note 7)			$ 0
Ending balance (in shares) at Dec. 31, 2020	0
Ending balance at Dec. 31, 2020	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options (in shares)	47,549			47,549
Exercise of stock options	$ 13				13
Stock-based compensation	2,694				2,694
Net exercise of common and preferred stock warrants (in shares)				32,120
Net exercise of common and preferred stock warrants	18				18
Issuance of stock under Employee Stock Purchase Plan (in shares)				11,649
Issuance of stock under Employee Stock Purchase Plan	142				142
Net loss	$ (16,687)					(16,687)
Ending balance (in shares) at Dec. 31, 2020	12,652,308			12,652,308
Ending balance at Dec. 31, 2020	$ 41,839			$ 13	$ 223,115	$ (181,289)