Revenue Arrangements - Narrative (Details) - USD ($) $ in Thousands	1 Months Ended			3 Months Ended		6 Months Ended
	Jan. 31, 2023	Oct. 31, 2021	Jun. 30, 2020	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022	Dec. 31, 2022	Dec. 31, 2021
Disaggregation of Revenue [Line Items]
Short-term contract liability				$ 4,234		$ 4,234		$ 593
Long-term contract liability				4,863		4,863		0
Revenue recognized						(1,996)
Accounts receivable				5,385		5,385		6,596
Collaboration and license revenue				5,249	$ 39,273	11,187	$ 73,272
Remaining performance obligation				9,100		9,100
SOBI Purchase Agreement
Disaggregation of Revenue [Line Items]
Revenue recognized				4,300	29,200
Accounts receivable				5,100		5,100		5,000
Collaboration and license revenue						8,700	52,900
SOBI Purchase Agreement | Unbilled Revenues
Disaggregation of Revenue [Line Items]
Accounts receivable				1,100		1,100		3,200
Takeda Agreement
Disaggregation of Revenue [Line Items]
Upfront cash payment		$ 3,000
Short-term contract liability				0		0		100
Asset, reclassified to receivable				500
Revenue recognized					0		1,000
Future additional payments, expected		$ 1,124,000
Collaboration and license revenue				100		$ 600
Collaborative Arrangement
Disaggregation of Revenue [Line Items]
Upfront cash payment			$ 75,000
Sales milestone payments			$ 630,000
Astellas Gene Therapies
Disaggregation of Revenue [Line Items]
Upfront payment	$ 10,000
Development and commercial milestones plus royalties	340,000
Reimbursement percentage, budgeted costs incurred to complete the development						25.00%
Upfront cash payment	10,000
Development cost reimbursements	$ 5,500
Short-term contract liability				4,200		$ 4,200
Long-term contract liability				4,900		4,900
Asset, reclassified to receivable						300
Revenue recognized				800		1,400
Sarepta Therapeutics, Inc.
Disaggregation of Revenue [Line Items]
Short-term contract liability								$ 500
Revenue recognized				$ 0	10,100	500	$ 10,200
Option term			24 months
Spark License Agreement
Disaggregation of Revenue [Line Items]
Short-term contract liability									$ 9,200
Revenue recognized					$ 0	$ 9,200