Fair Value Measurements - Schedule of Fair Value and Amortized Cost of Investments in Marketable Securities by Major Security Type (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	$ 805,154	$ 735,042
Unrealized Gain	50	57
Unrealized Loss	(96)	(13)
Fair Value	805,108	735,086
Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	310,482	146,468
Fair Value	310,482	146,468
U.S. Treasury Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	135,787	301,075
Unrealized Gain	11	38
Unrealized Loss	(39)	(1)
Fair Value	135,759	301,112
U.S. Government Agency Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost		24,997
Unrealized Gain		4
Fair Value		25,001
Corporate Securities and Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	358,885	262,502
Unrealized Gain	39	15
Unrealized Loss	(57)	(12)
Fair Value	$ 358,867	$ 262,505