Fair Value Measurements - Amortized Cost, Unrealized Gains and Losses, and Fair Value (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Debt Securities, Available-for-Sale, Fair Value to Amortized Cost, after Allowance for Credit Loss [Abstract]
Amortized Cost	$ 2,467,611	$ 2,350,988
Unrealized Gains	153	357
Unrealized Losses	(20,305)	(28,876)
Fair Value	2,447,459	2,322,469
Commercial paper
Debt Securities, Available-for-Sale, Fair Value to Amortized Cost, after Allowance for Credit Loss [Abstract]
Amortized Cost	88,960	0
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	88,960	0
U.S. government notes
Debt Securities, Available-for-Sale, Fair Value to Amortized Cost, after Allowance for Credit Loss [Abstract]
Amortized Cost	790,970	1,007,175
Unrealized Gains	34	3
Unrealized Losses	(7,491)	(13,223)
Fair Value	783,513	993,955
Corporate bonds
Debt Securities, Available-for-Sale, Fair Value to Amortized Cost, after Allowance for Credit Loss [Abstract]
Amortized Cost	1,059,915	1,125,920
Unrealized Gains	111	271
Unrealized Losses	(8,531)	(13,057)
Fair Value	1,051,495	1,113,134
Agency securities
Debt Securities, Available-for-Sale, Fair Value to Amortized Cost, after Allowance for Credit Loss [Abstract]
Amortized Cost	527,766	217,893
Unrealized Gains	8	83
Unrealized Losses	(4,283)	(2,596)
Fair Value	$ 523,491	$ 215,380