Fair Value Measurements - Summary of Financial Assets Recognized at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Mar. 31, 2026	Dec. 31, 2025
Marketable securities:
Investment in Kyverna Therapeutics, Inc.	$ 10,130	$ 11,034
Fair Value on Recurring Basis [Member]
Assets
Cash equivalents and restricted cash equivalents	79,145	92,263
Marketable securities:
Total marketable securities	382,550	449,670
Investment in Kyverna Therapeutics, Inc.	10,130	11,034
Total Assets	471,825	552,967
Fair Value on Recurring Basis [Member] \| U.S. Treasury and Other Government - Backed Securities [Member]
Marketable securities:
Total marketable securities	191,841	221,117
Fair Value on Recurring Basis [Member] \| Financial Institution Debt Securities [Member]
Marketable securities:
Total marketable securities	116,544	146,815
Fair Value on Recurring Basis [Member] \| Corporate Debt Securities [Member]
Marketable securities:
Total marketable securities	74,165	81,738
Fair Value on Recurring Basis [Member] \| Level 1 [Member]
Assets
Cash equivalents and restricted cash equivalents	79,145	92,263
Marketable securities:
Total marketable securities	129,324	150,852
Investment in Kyverna Therapeutics, Inc.	10,130	11,034
Total Assets	218,599	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	129,324	150,852
Fair Value on Recurring Basis [Member] \| Level 2 [Member]
Marketable securities:
Total marketable securities	253,226	298,818
Total Assets	253,226	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	62,517	70,265
Fair Value on Recurring Basis [Member] \| Level 2 [Member] \| Financial Institution Debt Securities [Member]
Marketable securities:
Total marketable securities	116,544	146,815
Fair Value on Recurring Basis [Member] \| Level 2 [Member] \| Corporate Debt Securities [Member]
Marketable securities:
Total marketable securities	$ 74,165	$ 81,738