Fair Value Measurements - Financial Assets Measured at Fair Value on a Recurring Basis by Level Within Fair Value Hierarchy (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022	Sep. 30, 2022
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents	$ 452,100	$ 848,631	$ 963,735
Amortized Cost	1,711,677	2,403,183
Gross Unrealized Holding Gains	29	0
Gross Unrealized Holding Losses	(1,229)	(8,396)
Aggregate Fair Value	1,721,302	2,426,679
Level 1 | Money market funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	470,323	909,342
Cash and cash equivalents	470,323	909,342
Restricted cash equivalents	20,300	19,300
Level 1 | Equity securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Equity securities	10,825	31,892
Level 2 | U.S. government treasuries
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	1,073,982	1,493,841
Gross Unrealized Holding Gains	15	0
Gross Unrealized Holding Losses	(1,009)	(8,396)
Aggregate Fair Value	1,072,988	$ 1,485,445
Level 2 | U.S. government agency bonds and discount notes
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	167,372
Gross Unrealized Holding Gains	14
Gross Unrealized Holding Losses	(220)
Aggregate Fair Value	$ 167,166