License Agreements - Additional Information (Detail) £ in Thousands, $ in Thousands						1 Months Ended	3 Months Ended		6 Months Ended		12 Months Ended
	Sep. 30, 2020 USD ($)	Sep. 30, 2020 GBP (£)	Oct. 02, 2017 USD ($)	Jan. 27, 2016 USD ($)	Jan. 27, 2016 CAD ($) shares	Aug. 31, 2017 USD ($) shares	Jun. 30, 2022 USD ($) shares	Jun. 30, 2021 USD ($)	Jun. 30, 2022 USD ($) shares	Jun. 30, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2021 shares	Nov. 17, 2016 USD ($)
License Agreement [Line Items]
Collaborative agreement expenses							$ 417,000	$ 825,000	$ 1,380,000	$ 825,000
Common stock, issued | shares							43,696,000		43,696,000				43,652,000
Research and development							$ 18,877,000	22,544,000	$ 38,130,000	41,024,000
University of Manchester Agreement [Member] | MPSII License Agreement [Member]
License Agreement [Line Items]
Upfront license fee											$ 8,000,000
Milestone payments payable	$ 80,000,000
Milestone payment paid	2,000,000
Milestone payment due	$ 4,000,000
Agreement Expiration Period									15 years
Agreement Expiration Description									upon the later of 15 years from the effective date or the expiration of the last valid claim of the licensed patent
Research and development expense | £		£ 9,900
UHN Agreement [Member]
License Agreement [Line Items]
Research and development expense							0	24,000	$ 24,000	68,000
Milestone fees							0	0
UHN Agreement [Member] | Fabry License Agreement [Member]
License Agreement [Line Items]
Upfront license fee					$ 75
Milestone payments payable					2,450
Option fee					20
UHN Agreement [Member] | Interleukin 12 License Agreement [Member]
License Agreement [Line Items]
Upfront license fee					264
Milestone payments payable					19,275
Milestone fees							0	0	0	0
Annual maintenance fees					$ 50
Common stock, issued | shares					1,161,665,000
Fair value of shares issued				$ 480,000
Payments upon closing of an initial public offering				$ 2,000,000								$ 2,000,000
Research and development							39,000	0	39,000	39,000
BioMarin Pharmaceutical Inc [Member]
License Agreement [Line Items]
Upfront license fee						$ 500,000
Preferred stock issued | shares						233,765,000
Milestone payments							13,000,000
Expenses related to license							0	0	0	0
GenStem Therapeutics Inc [Member]
License Agreement [Line Items]
Upfront license fee			$ 1,000,000
Milestone payments payable			$ 16,000,000
Expenses related to license							0	0	0	0
Lund University Rights Holders Agreement [Member]
License Agreement [Line Items]
Milestone payments payable														$ 550,000
Expenses related to license							$ 0	$ 0	$ 0	$ 0