Collaborative Arrangements - Takeda (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	May 31, 2021	Mar. 31, 2020
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contract liabilities: deferred revenue	$ 30,609	$ 6,335
Takeda
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contract liabilities: deferred revenue	900	2,200
Revenue recognized, including opening balance	$ 4,900	$ 7,400	$ 13,200
Takeda | Up-front Payment
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contract liabilities: deferred revenue					$ 8,500
Takeda | Research and Development Reimbursement, Three Initial Programs
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contingent receivable				$ 10,500
Takeda | Research and Development Reimbursement, Fourth Program
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contingent receivable				3,400
Takeda | Milestone Payment Per Target Gene
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contingent receivable				$ 104,000