Stockholders' Deficit - Additional Information (Details)			3 Months Ended		9 Months Ended
	Jul. 14, 2020 USD ($) $ / shares shares	Jul. 01, 2020 USD ($) $ / shares shares	Sep. 30, 2020 Vote $ / shares shares	Sep. 30, 2019 USD ($) shares	Sep. 30, 2020 USD ($) Vote $ / shares shares	Sep. 30, 2019 USD ($) shares	Jun. 30, 2020 shares	Mar. 31, 2020 shares	Dec. 31, 2019 USD ($) shares	Aug. 31, 2019 USD ($)	Aug. 26, 2019 $ / shares shares	Jun. 30, 2019 shares	Mar. 31, 2019 shares	Dec. 31, 2018 shares
Class Of Stock [Line Items]
Capital stock, shares authorized											126,270,161
Common stock, shares authorized		100,000,000	100,000,000		100,000,000						71,919,982
Common stock, par value | $ / shares		$ 0.0001	$ 0.0001		$ 0.0001						$ 0.0001
Preferred stock, shares authorized		54,350,179									54,350,179
Preferred stock, par value | $ / shares		$ 0.0001									$ 0.0001
Proceeds from issuance of convertible preferred stock | $						$ 5,986,000
Estimated fair value of preferred stock purchase right liability | $		$ 41,600,000							$ 1,478,000	$ 2,800,000
Change in fair value of Series B convertible preferred stock purchase right liability | $				$ 3,383,000	$ (40,163,000)	$ 3,383,000
Proceeds from initial public offering, net of issuance costs | $					$ 265,461,000
Shares issued during period			32,568,332		32,568,332				1,600,601
Common stock, shares outstanding			32,568,332		32,568,332				1,600,601
Cash dividends declared or paid | $					$ 0
Common stock, voting rights					Each holder of common stock is entitled to one vote for each share on all matters submitted to a vote of the stockholders, including the election of directors.
Common stock entitled, number of vote for each share | Vote			1		1
IPO
Class Of Stock [Line Items]
Proceeds from initial public offering, net of issuance costs | $	$ 265,100,000	$ 265,100,000
Shares issued during period	16,100,000
Underwriters Option to Purchase Additional Shares
Class Of Stock [Line Items]
Shares issued during period	2,100,000
Common Stock
Class Of Stock [Line Items]
Conversion of convertible preferred stock into common stock			14,689,215
Issuance of common stock upon initial public offering, net of issuance cost, Shares			16,100,000
Common Stock | IPO
Class Of Stock [Line Items]
Conversion of convertible preferred stock into common stock	14,689,215
Issuance of common stock upon initial public offering, net of issuance cost, Shares	16,100,000
Stock public offering price | $ / shares	$ 18.00
Proceeds from initial public offering, net of issuance costs | $	$ 265,100,000
Common Stock | Underwriters Option to Purchase Additional Shares
Class Of Stock [Line Items]
Issuance of common stock upon initial public offering, net of issuance cost, Shares	2,100,000
Series A Convertible Preferred Stock
Class Of Stock [Line Items]
Preferred stock, shares authorized											6,170,349
Series B Convertible Preferred Stock
Class Of Stock [Line Items]
Preferred stock, shares authorized											48,179,830
Number of shares converted into shares		10
Number of shares converted into shares		1
Temporary equity, issuance of Series B second tranche convertible preferred stock, net of issuance costs, Shares		27,066,206
Proceeds from issuance of convertible preferred stock | $		$ 64,400,000
Series B Convertible Preferred Stock | Stock Purchase Agreement
Class Of Stock [Line Items]
Number of convertible preferred stock sold and issued during the period		27,066,206
Gross proceed from convertible preferred stock | $		$ 64,400,000
Convertible Preferred Stock
Class Of Stock [Line Items]
Temporary equity, issuance of Series B second tranche convertible preferred stock, net of issuance costs, Shares			27,066,206	18,817,499
Convertible preferred stock, outstanding			0	24,987,848	0	24,987,848	27,283,973	27,283,973	27,283,973			6,170,349	6,170,349	6,170,349
Convertible Preferred Stock | Common Stock | IPO
Class Of Stock [Line Items]
Conversion of convertible preferred stock into common stock	14,689,215