Consolidated 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	$ (474,186)	$ (267,892)	$ (134,231)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	7,572	6,891	6,311
(Gain) loss on disposal of property and equipment	(162)	0	35
Equity-based compensation	91,400	47,009	19,903
Amortization of investment premiums	4,003	7,604	538
Loss from equity method investment	11,079	1,325	0
Deferral of equity method investment intra-entity profit on sales	11,405	2,937	0
Change in fair value of contingent consideration	13,485	0	0
In-process research and development charge	55,990	0	0
Changes in operating assets and liabilities:
Accounts receivable	(1,737)	99	2,490
Prepaid expenses and other current assets	(2,160)	(9,798)	(9,206)
Operating lease right-of-use assets	13,121	9,349	6,457
Other assets	(1,091)	117	83
Accounts payable	(4,584)	529	5,060
Accrued expenses	15,924	17,260	13,031
Deferred revenue	(63,464)	(31,355)	45,121
Operating lease liabilities	(9,882)	(9,105)	(5,504)
Net cash used in operating activities	(333,287)	(225,030)	(49,912)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(13,558)	(12,756)	(3,585)
Purchases of marketable securities	(429,032)	(1,020,620)	(473,702)
Maturities of marketable securities	647,581	485,598	262,800
Proceeds from sale of property and equipment	150	0	0
Acquired in-process research and development, net of cash acquired of $287	(44,832)	0	0
Investment in Kyverna Therapeutics, Inc.	0	(3,000)	0
Net cash provided by (used in) investing activities	160,309	(550,778)	(214,487)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from options exercised	14,517	41,094	11,574
Issuance of shares through employee stock purchase plan	2,649	2,024	1,557
Net cash provided by financing activities	582,955	736,688	371,779
Net increase (decrease) in cash and cash equivalents and restricted cash equivalents	409,977	(39,120)	107,380
Cash and cash equivalents and restricted cash equivalents, beginning of period	125,486	164,606	57,226
Cash and cash equivalents and restricted cash equivalents, end of period	535,463	125,486	164,606
Reconciliation of cash, cash equivalents and restricted cash equivalents to consolidated balance sheet:
Cash and cash equivalents	523,506	123,406	160,020
Restricted cash equivalents, included in investments and other assets	11,957	2,080	4,586
Total cash and cash equivalents and restricted cash equivalents	535,463	125,486	164,606
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION:
Purchases of property and equipment unpaid at period end	1,623	667	1,508
Right-of-use assets acquired under operating leases	67,053	49,378	26,432
Contingent consideration liability assumed in asset acquisition	10,541	0	0
Non-cash Trade-in Of Property and Equipment	200	0	0
Regeneron Pharmaceuticals Inc. [Member]
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock	0	0	12,580
AvenCell Therapeutics, Inc [Member]
Adjustments to reconcile net loss to net cash used in operating activities:
Loss from equity method investment	(11,400)	(2,900)
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION:
Non-cash contribution of intellectual property	0	62,900	0
Sparing Vision SAS [Member]
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION:
Non-cash contribution of intellectual property	0	14,759	0
Kyverna Therapeutics, Inc. [Member]
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION:
Non-cash contribution of intellectual property	0	7,000	0
Follow On Public Offering
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock	337,892	648,315	296,607
At The Market Offerings
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock	$ 227,897	$ 45,255	$ 49,461