Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (481,192)	$ (474,186)	$ (267,892)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	8,976	7,572	6,891
Loss (gain) on disposal of property and equipment	72	(162)	0
Stock-based compensation	134,050	91,400	47,009
(Accretion) amortization of investment discounts and premiums	(25,897)	4,003	7,604
Loss from equity method investment	15,633	11,079	1,325
Deferral of equity method investment intra-entity profit on sales	6,624	11,405	2,937
Change in fair value of contingent consideration	100	13,485	0
In-process research and development expense	0	55,990	0
Changes in operating assets and liabilities:
Accounts receivable	(32,688)	(1,737)	99
Prepaid expenses and other current assets	(27,168)	(2,160)	(9,798)
Operating lease right-of-use assets	19,011	13,121	9,349
Other assets	(707)	(1,091)	117
Accounts payable	2,522	(4,584)	529
Accrued expenses	6,024	15,924	17,260
Deferred revenue	(2,778)	(63,464)	(31,355)
Operating lease liabilities	(16,668)	(9,882)	(9,105)
Net cash used in operating activities	(394,086)	(333,287)	(225,030)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(13,985)	(13,558)	(12,756)
Purchases of marketable securities	(904,464)	(429,032)	(1,020,620)
Maturities of marketable securities	887,102	647,581	485,598
Proceeds from sale of property and equipment	0	150	0
Acquired in-process research and development, net of cash acquired of $287	0	(44,832)	0
Investment in Kyverna Therapeutics, Inc.	0	0	(3,000)
Net cash (used in) provided by investing activities	(31,347)	160,309	(550,778)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from options exercised	6,599	14,517	41,094
Issuance of shares through employee stock purchase plan	3,929	2,649	2,024
Net cash provided by financing activities	130,323	582,955	736,688
Net (decrease) increase in cash and cash equivalents and restricted cash equivalents	(295,110)	409,977	(39,120)
Cash, cash equivalents and restricted cash equivalents, beginning of period	535,463	125,486	164,606
Cash, cash equivalents and restricted cash equivalents, end of period	240,353	535,463	125,486
Reconciliation of cash, cash equivalents and restricted cash equivalents to consolidated balance sheet:
Cash and cash equivalents	226,748	523,506	123,406
Restricted cash equivalents, included in investments and other assets	13,605	11,957	2,080
Total cash, cash equivalents and restricted cash equivalents	240,353	535,463	125,486
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION:
Purchases of property and equipment unpaid at period end	1,525	1,623	667
Shares issued for Rewrite contingent consideration	24,126	0	0
Right-of-use assets acquired under operating leases	1,311	67,053	49,378
Proceeds from at-the-market offerings unpaid at period end	2,075	0	0
Contingent consideration liability assumed in asset acquisition	0	10,541	0
Non-cash trade-in of property and equipment	0	200	0
AvenCell Therapeutics, Inc [Member]
Adjustments to reconcile net loss to net cash used in operating activities:
Loss from equity method investment	(6,600)	(11,400)	(2,900)
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION:
Non-cash contribution of intellectual property	0	0	62,900
Sparing Vision SAS [Member]
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION:
Non-cash contribution of intellectual property	0	0	14,759
Kyverna Therapeutics, Inc. [Member]
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION:
Non-cash contribution of intellectual property	0	0	7,000
Follow On Public Offering
CASH FLOWS FROM FINANCING ACTIVITIES:
Net proceeds from issuance of common stock	0	337,892	648,315
At The Market Offerings
CASH FLOWS FROM FINANCING ACTIVITIES:
Net proceeds from issuance of common stock	$ 119,795	$ 227,897	$ 45,255