Convertible Preferred Stock and Stockholders' Equity (Deficit) - Additional Information (Details) - USD ($)							1 Months Ended			12 Months Ended
	Feb. 12, 2019	Sep. 06, 2018	Jul. 20, 2018	May 21, 2018	Jan. 04, 2018	Dec. 03, 2015	Mar. 31, 2018	Jan. 31, 2018	Nov. 30, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Stockholders Equity Deficit [Line Items]
Issuance of common stock in connection with a public offering,net of underwriting discounts,commissions,and offering costs										$ 291,311,000
Common stock, voting right										one
Shares of common stock, repurchase										4,648,526	7,482,032	1,305,421
Founder
Stockholders Equity Deficit [Line Items]
Issuance price per share		$ 9.63		$ 2.61
Sale of shares of common stock		1,795,023		251,547
Percentage of fully diluted share capital										15.00%
Increased in equity capital amount										$ 300,000,000
Additional shares of restricted stock subject to vesting restrictions		1,795,023		251,547
Common Stock
Stockholders Equity Deficit [Line Items]
Sale of shares of common stock										19,837,500
Issuance of common stock in connection with a public offering,net of underwriting discounts,commissions,and offering costs										$ 2,000
Unrestricted shares of common stock were subject to service vesting conditions											4,580,444
Founder Shares
Stockholders Equity Deficit [Line Items]
Issuance price per share						$ 0.0001
Sale of shares of common stock						9,160,888
Issuance of common stock in connection with a public offering,net of underwriting discounts,commissions,and offering costs						$ 4,100
Common Stock vesting percentage					50.00%
Common stock vesting period					5 years
Common Stock | Stock Restriction Agreements
Stockholders Equity Deficit [Line Items]
Unrestricted shares of common stock were subject to service vesting conditions								4,580,444
Initial Public Offering ("IPO")
Stockholders Equity Deficit [Line Items]
Sale of shares of common stock	19,837,500
Series Seed Convertible Preferred Stock | Initial Public Offering ("IPO") | Common Stock
Stockholders Equity Deficit [Line Items]
Conversion of preferred stock into common stock										30,493,460
Series Seed Convertible Preferred Stock | AA Biopharma Inc.
Stockholders Equity Deficit [Line Items]
Convertible Preferred Stock Issued					20,000,000
Preferred Stock, Conversion Basis					On January 4, 2018, the Company issued an aggregate of 20,000,000 shares of Series Seed Convertible Preferred Stock in connection with the merger agreement with AA Biopharma Inc.
Shares Issuable upon Conversion of Series A Convertible Preferred Stock
Stockholders Equity Deficit [Line Items]
Convertible Preferred Stock Issued							45,714,286	45,714,286
Issuance price per share							$ 1.75	$ 1.75
Preferred stock, gross proceeds							$ 73,900,000	$ 73,900,000
Conversion of principal amount into preferred stock							$ 6,100,000	$ 6,100,000
Shares Issuable upon Conversion of Series A Convertible Preferred Stock | Initial Public Offering ("IPO") | Common Stock
Stockholders Equity Deficit [Line Items]
Conversion of preferred stock into common stock										30,493,460
Series B Convertible Preferred Stock
Stockholders Equity Deficit [Line Items]
Convertible Preferred Stock Issued			71,506,513
Issuance price per share			$ 3.2167
Proceeds from issuance of convertible preferred stock, net			$ 230,000,000
Shares Issuable upon Conversion of Series B Convertible Preferred Stock | Initial Public Offering ("IPO") | Common Stock
Stockholders Equity Deficit [Line Items]
Conversion of preferred stock into common stock										30,493,460
Series A Convertible Preferred Stock
Stockholders Equity Deficit [Line Items]
Convertible Preferred Stock Issued											42,215,077
Proceeds from issuance of convertible preferred stock, net											$ 73,491,000
Series A Convertible Preferred Stock | Stock Restriction Agreements
Stockholders Equity Deficit [Line Items]
Shares subject to forfeiture									1,305,421