Fair Value Measurements and Fair Value of Financial Instruments - Schedule of Financial Instruments Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Investments:
Fair Value	$ 2,222,850
Fair value, recurring
Cash and cash equivalents:
Amortized Cost	1,050,225	$ 397,616
Gross Unrealized Gains	17	0
Gross Unrealized Losses	(53)	(165)
Fair Value	1,050,189	397,451
Investments:
Amortized Cost	2,216,389	845,109
Gross Unrealized Gains	7,122	615
Gross Unrealized Losses	(661)	(273)
Fair Value	2,222,850	845,451
Total assets measured at fair value, amortized cost	3,266,614	1,242,725
Total assets measured at fair value, gross unrealized gains	7,139	615
Total assets measured at fair value, gross unrealized losses	(714)	(438)
Total assets measured at fair value, fair value	3,273,039	1,242,902
Fair value, recurring | Cash | Level 1
Cash and cash equivalents:
Amortized Cost	25,939	50,003
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	25,939	50,003
Fair value, recurring | Money market funds | Level 1
Cash and cash equivalents:
Amortized Cost	463,700	47,357
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	463,700	47,357
Fair value, recurring | U.S. Treasury securities | Level 1
Cash and cash equivalents:
Amortized Cost	75,578
Gross Unrealized Gains	7
Gross Unrealized Losses	(3)
Fair Value	75,582
Investments:
Amortized Cost	1,124,838	481,704
Gross Unrealized Gains	3,341	422
Gross Unrealized Losses	(452)	(44)
Fair Value	1,127,727	482,082
Fair value, recurring | Commercial paper | Level 2
Cash and cash equivalents:
Amortized Cost	466,099	300,256
Gross Unrealized Gains	8	0
Gross Unrealized Losses	(49)	(165)
Fair Value	466,058	300,091
Fair value, recurring | Commercial paper | Level 2
Investments:
Amortized Cost	128,620	102,435
Gross Unrealized Gains	141	7
Gross Unrealized Losses	0	(35)
Fair Value	128,761	102,407
Fair value, recurring | U.S. government agency securities | Level 2
Cash and cash equivalents:
Amortized Cost	18,909
Gross Unrealized Gains	2
Gross Unrealized Losses	(1)
Fair Value	18,910
Investments:
Amortized Cost	198,955	103,484
Gross Unrealized Gains	769	0
Gross Unrealized Losses	(61)	(152)
Fair Value	199,663	103,332
Fair value, recurring | Corporate debt | Level 2
Investments:
Amortized Cost	603,485	133,523
Gross Unrealized Gains	2,427	168
Gross Unrealized Losses	(133)	(42)
Fair Value	605,779	133,649
Fair value, recurring | Asset-backed securities | Level 2
Investments:
Amortized Cost	160,491	23,963
Gross Unrealized Gains	444	18
Gross Unrealized Losses	(15)	0
Fair Value	$ 160,920	$ 23,981