Stockholders' Equity - Additional Information (Detail) - USD ($)							1 Months Ended			12 Months Ended
	Jul. 02, 2021	Jun. 29, 2021	Dec. 04, 2020	Dec. 01, 2020	Jun. 05, 2020	Jun. 01, 2020	May 31, 2020	Aug. 31, 2019	Oct. 31, 2018	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Class Of Stock [Line Items]
Common stock, par value										$ 0.0001	$ 0.0001
Proceeds from common stock offering										$ 1,817,900,000
Common Stock, Par or Stated Value Per Share										$ 0.0001	$ 0.0001
Regeneron Pharmaceuticals Inc. [Member]
Class Of Stock [Line Items]
Proceeds from common stock offering										$ 0	$ 12,580,000	$ 0
Issuance of common stock											$ 12,580,000
2018 Sales Agreement [Member]
Class Of Stock [Line Items]
Stock Issued During Period, Shares, New Issues									5,890,648
Common stock price per share									$ 16.98
Proceeds from common stock offering									$ 96,400,000
Percentage of gross proceeds from common stock as sales agent cash commission										3.00%
Shares Issued, Price Per Share									$ 16.98
2018 Sales Agreement [Member] | General and Administrative Expenses [Member]
Class Of Stock [Line Items]
Legal accounting and other fees									$ 600,000
2018 Sales Agreement [Member] | Maximum [Member]
Class Of Stock [Line Items]
Proceeds from common stock offering									$ 100,000,000.0
2019 Sales Agreement [Member]
Class Of Stock [Line Items]
Stock Issued During Period, Shares, New Issues										641,709	2,270,161	287,231
Common stock price per share										$ 72.79	$ 22.53	$ 16.48
Proceeds from common stock offering										$ 45,300,000	$ 49,500	$ 4,400,000
Percentage of gross proceeds from common stock as sales agent cash commission									3.00%
Proceeds from common stock offering										$ 47,400,000
Shares Issued, Price Per Share										$ 72.79	$ 22.53	$ 16.48
2019 Sales Agreement [Member] | General and Administrative Expenses [Member]
Class Of Stock [Line Items]
Legal accounting and other fees										$ 100	$ 200,000	$ 200,000
2019 Sales Agreement [Member] | Maximum [Member]
Class Of Stock [Line Items]
Proceeds from common stock offering								$ 150,000.0
Follow On Public Offering
Class Of Stock [Line Items]
Proceeds from common stock offering										648,315,000	296,607,000	$ 0
Issuance of common stock										$ 648,315,000	$ 296,607,000
Follow On Public Offering | Underwriting Agreement [Member]
Class Of Stock [Line Items]
Stock Issued During Period, Shares, New Issues		4,758,620		5,513,699		6,301,370
Common stock, par value		$ 0.0001		$ 0.0001		$ 0.0001
Shares available for future issuance		620,689		719,178		821,917
Common stock price per share		$ 145.00		$ 36.50		$ 18.25
Proceeds from common stock offering	$ 648,300,000		$ 188,900,000		$ 107,700,000
Shares Issued, Price Per Share		145.00		36.50		18.25
Common Stock, Par or Stated Value Per Share		$ 0.0001		$ 0.0001		$ 0.0001
Private Placement [Member] | 2020 Stock Purchase Agreement [Member] | Regeneron Pharmaceuticals Inc. [Member]
Class Of Stock [Line Items]
Stock Issued During Period, Shares, New Issues							925,218
Common stock, par value							$ 0.0001
Cash consideration received on sale of common stock							$ 30,000,000.0
Sale of stock, price per share							$ 32.42
Percentage of premium over volume-weighted average trading price of common stock during 30-day period prior to closing of equity transaction							100.00%
Issuance of common stock							$ 12,600,000
Sale of Stock, Consideration Received on Transaction							$ 30,000,000.0
Common Stock, Par or Stated Value Per Share							$ 0.0001