Stockholders' Equity (Details Textual) - USD ($) $ / shares in Units, $ in Thousands		1 Months Ended	12 Months Ended
	Jun. 19, 2019	May 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Nov. 25, 2020	Nov. 24, 2020
Class Of Stock [Line Items]
Common stock, shares authorized			60,000,000	30,000,000		60,000,000	30,000,000
Proceeds from issuance of common stock, net of issuance costs			$ 423,819	$ 21,278
Common stock, shares issued			26,192,000	15,138,000
Common stock, par value			$ 0.001	$ 0.001
Antidilutive securities excluded from computation of earnings per share			1,157,175	138,377	94,000
Unvested Restricted Ordinary Shares [Member]
Class Of Stock [Line Items]
Antidilutive securities excluded from computation of earnings per share				622,667	622,667
Ultragenyx [Member]
Class Of Stock [Line Items]
Common stock, shares issued		600,000,000
Common stock, price per share		$ 16.00
Proceeds from issuance of common stock on option exercise		$ 9,600
Equity Purchase Agreement [Member] | Collaboration Partner - Expanded Ultragenyx [Member]
Class Of Stock [Line Items]
Common stock, shares issued	2,400,000
Common stock, par value	$ 0.001
Common stock purchase price per share	$ 10.00
Common stock shares restricted from selling period subsequent to issuance date	2 years
Purchase of additional shares of common stock	600,000
Purchase of additional shares of common stock price per share	$ 16.00
Underwritten Public Offering [Member]
Class Of Stock [Line Items]
Issuance of common stock			10,058,820,000
Common stock, price per share, Offering one			$ 17.00
Common stock, price per share, Offering two			53.00
Common stock, price per share, Offering three			$ 110.00
Proceeds from issuance of common stock, gross			$ 452,100
Offering costs			28,300
Proceeds from issuance of common stock, net of issuance costs			$ 423,800