Stockholders' Equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands		1 Months Ended				3 Months Ended		6 Months Ended
	Oct. 22, 2020	Mar. 31, 2021	Dec. 31, 2020	Oct. 31, 2020	Jul. 31, 2019	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Nov. 30, 2020
Class Of Stock [Line Items]
Common stock warrants exercise price per share										$ 3.29
Gross proceeds from private placement					$ 59,977
Proceeds from issuance of common stock								$ 134,878
Ultragenyx [Member] | Collaborative Arrangement, Transaction with Party to Collaborative Arrangement [Member]
Class Of Stock [Line Items]
Common stock issued price per share	$ 5.1113
Issued and sold shares of common stock	7,825,797
Proceeds from issuance of common stock	$ 40,000
Private Placement [Member]
Class Of Stock [Line Items]
Offering costs			$ 3,790		$ 2,102
ATM Sales Agreement [Member]
Class Of Stock [Line Items]
Stock issued and sold				6,309,632
Proceeds from issuance of common stock				$ 23,209
Public Offering [Member]
Class Of Stock [Line Items]
Stock issued and sold		25,000,000
Common stock issued price per share		$ 5.575
Proceeds from issuance of common stock		$ 134,878
Common Stock [Member]
Class Of Stock [Line Items]
Stock issued and sold								25,000,000
Common Stock [Member] | Private Placement [Member]
Class Of Stock [Line Items]
Stock issued and sold			24,324,320		10,607,525
Common stock issued price per share			$ 3.70		$ 4.65
Net proceeds from private placement			$ 86,210
Pre-Funded Warrants [Member]
Class Of Stock [Line Items]
Warrants exercised				137,460		0	0	0	0
Pre-Funded Warrants [Member] | Private Placement [Member]
Class Of Stock [Line Items]
Warrants to purchase common stock					2,295,699
Warrants price per share					$ 4.64
Warrants exercisable for common stock					1
Common stock warrants exercise price per share					$ 0.01