Fair Value Measurements - Summary of Financial Assets Recognized at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Jun. 30, 2026	Dec. 31, 2025
Marketable securities:
Investment in Kyverna Therapeutics, Inc.	$ 10,459	$ 11,034
Fair Value on Recurring Basis [Member]
Assets
Cash equivalents and restricted cash equivalents	78,641	92,263
Marketable securities:
Total marketable securities	522,226	449,670
Investment in Kyverna Therapeutics, Inc.	10,459	11,034
Total Assets	611,326	552,967
Fair Value on Recurring Basis [Member] \| U.S. Treasury and Other Government - Backed Securities [Member]
Marketable securities:
Total marketable securities	275,645	221,117
Fair Value on Recurring Basis [Member] \| Financial Institution Debt Securities [Member]
Marketable securities:
Total marketable securities	168,784	146,815
Fair Value on Recurring Basis [Member] \| Corporate Debt Securities [Member]
Marketable securities:
Total marketable securities	77,797	81,738
Fair Value on Recurring Basis [Member] \| Level 1 [Member]
Assets
Cash equivalents and restricted cash equivalents	78,641	92,263
Marketable securities:
Total marketable securities	184,124	150,852
Investment in Kyverna Therapeutics, Inc.	10,459	11,034
Total Assets	273,224	254,149
Fair Value on Recurring Basis [Member] \| Level 1 [Member] \| U.S. Treasury and Other Government - Backed Securities [Member]
Marketable securities:
Total marketable securities	184,124	150,852
Fair Value on Recurring Basis [Member] \| Level 2 [Member]
Marketable securities:
Total marketable securities	338,102	298,818
Total Assets	338,102	298,818
Fair Value on Recurring Basis [Member] \| Level 2 [Member] \| U.S. Treasury and Other Government - Backed Securities [Member]
Marketable securities:
Total marketable securities	91,521	70,265
Fair Value on Recurring Basis [Member] \| Level 2 [Member] \| Financial Institution Debt Securities [Member]
Marketable securities:
Total marketable securities	168,784	146,815
Fair Value on Recurring Basis [Member] \| Level 2 [Member] \| Corporate Debt Securities [Member]
Marketable securities:
Total marketable securities	$ 77,797	$ 81,738