Fair Value Measurements - Summary of Financial Assets Recognized at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Marketable securities:
Investment in Kyverna Therapeutics, Inc.	$ 5,740	$ 10,000
Fair Value on Recurring Basis [Member]
Assets
Cash equivalents and restricted cash equivalents	93,355	136,254
Marketable securities:
Marketable securities	824,186	785,339
Investment in Kyverna Therapeutics, Inc.	5,740
Total Assets	923,281	921,593
Fair Value on Recurring Basis [Member] \| U.S. Treasury and Other Government - Backed Securities [Member]
Marketable securities:
Marketable securities	434,289	382,308
Fair Value on Recurring Basis [Member] \| Financial Institution Debt Securities [Member]
Marketable securities:
Marketable securities	249,607	246,119
Fair Value on Recurring Basis [Member] \| Corporate Debt Securities [Member]
Marketable securities:
Marketable securities	104,739	97,408
Fair Value on Recurring Basis [Member] \| Other Asset Backed Securities [Member]
Marketable securities:
Marketable securities	35,551	59,504
Fair Value on Recurring Basis [Member] \| Level 1 [Member]
Assets
Cash equivalents and restricted cash equivalents	93,355	136,254
Marketable securities:
Marketable securities	199,705	120,556
Investment in Kyverna Therapeutics, Inc.	5,740
Total Assets	298,800	256,810
Fair Value on Recurring Basis [Member] \| Level 1 [Member] \| U.S. Treasury and Other Government - Backed Securities [Member]
Marketable securities:
Marketable securities	199,705	120,556
Fair Value on Recurring Basis [Member] \| Level 2 [Member]
Marketable securities:
Marketable securities	624,481	664,783
Total Assets	624,481	664,783
Fair Value on Recurring Basis [Member] \| Level 2 [Member] \| U.S. Treasury and Other Government - Backed Securities [Member]
Marketable securities:
Marketable securities	234,584	261,752
Fair Value on Recurring Basis [Member] \| Level 2 [Member] \| Financial Institution Debt Securities [Member]
Marketable securities:
Marketable securities	249,607	246,119
Fair Value on Recurring Basis [Member] \| Level 2 [Member] \| Corporate Debt Securities [Member]
Marketable securities:
Marketable securities	104,739	97,408
Fair Value on Recurring Basis [Member] \| Level 2 [Member] \| Other Asset Backed Securities [Member]
Marketable securities:
Marketable securities	$ 35,551	$ 59,504

Fair value portion of asset recognized for present right to economic benefit.

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Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

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Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 820
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Fair value portion of investments in an entity not consolidated. Includes, but is not limited to, investments in an entity that is affiliated with the reporting entity by means of direct or indirect ownership, an entity in which the reporting entity shares control of the entity with another party or group, an entity which the company has significant influence, but does not have control and subsidiaries that are not required to be consolidated and are accounted for using the equity or cost method.

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