Consolidated and Combined Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Cash flows from operating activities:
Net loss	$ (254,153)	$ (292,213)	$ (120,114)
Adjustments to reconcile net loss to net cash used in operating activities:
Change in fair value of contingent consideration	232	439	(6,468)
Depreciation and amortization	11,533	16,350	13,188
Stock-based compensation expense	41,040	54,629	60,997
Other non-cash items	85	430	73
Changes in operating assets and liabilities:
Prepaid expenses and other assets	(8,356)	1,578	1,526
Operating lease right-of-use assets	34,649	15,541	13,764
Accounts payable	327	(6)	(13,240)
Accrued expenses and other liabilities	(8,110)	15,733	(7,479)
Operating lease liabilities	(12,042)	(16,199)	(10,960)
Deferred revenue	(22,762)	4,180	8,317
Collaboration research advancement	(19,577)	(7,496)	(7,397)
Net cash used in operating activities	(237,134)	(207,034)	(67,793)
Cash flows from investing activities:
Purchases of property, plant and equipment	(22,842)	(11,575)	(22,261)
Purchases of marketable securities	(145,908)	0	0
Proceeds from maturities of marketable securities	180,447	34,986	0
Purchase of intangible assets	0	(8,000)	0
Net cash provided by (used in) investing activities	11,697	15,411	(22,261)
Cash flows from financing activities:
Transfers from bluebird bio	0	354,889	90,054
Proceeds from issuance of common stock in private placement, net of issuance costs	165,533	0	0
Proceeds from exercise of stock options and ESPP contributions	696	0	0
Net cash provided by financing activities	166,229	354,889	90,054
Decrease in cash, cash equivalents and restricted cash	(59,208)	163,266	0
Cash, cash equivalents and restricted cash at beginning of year	163,266	0	0
Cash, cash equivalents and restricted cash at end of year	104,058	163,266	0
Reconciliation of cash, cash equivalents and restricted cash:
Cash and cash equivalents	71,032	130,414	0
Restricted cash included in restricted cash and other non-current assets	33,026	32,852	0
Total cash, cash equivalents and restricted cash	104,058	163,266	0
Supplemental cash flow disclosures:
Purchases of property, plant and equipment included in accounts payable and accrued expenses	10,896	3,703	2,039
Right-of-use assets obtained in exchange for operating lease liabilities	0	0	4,989
Non-cash return of bRT-related assets to bluebird bio	0	110,300	0
Increase of right-of-use asset and associated lease liability due to lease reassessment	0	174,618	0
Issuance of unrestricted stock awards to settle accrued employee compensation	$ 0	$ 6,544	$ 0