Fair Value Measurements - Schedule of Financial Assets Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities, fair value	$ 1,537,355	$ 1,456,098
Recurring Basis [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Other non-current assets	2,212	2,212
Total	2,223,473	2,381,341
Recurring Basis [Member] | Cash [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents	138,791	405,648
Recurring Basis [Member] | Money Market Funds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents	416,688	507,386
Recurring Basis [Member] | Corporate Debt Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents	11,824
Marketable securities, fair value	1,150,184	1,168,766
Recurring Basis [Member] | Certificates of Deposit [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents	116,603
Marketable securities, fair value	57,631	45,164
Recurring Basis [Member] | Commercial Paper [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents		9,997
Marketable securities, fair value	304,620	212,719
Recurring Basis [Member] | US Treasury Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities, fair value	11,857	16,192
Recurring Basis [Member] | Government-sponsored Enterprise Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities, fair value	13,063	13,257
Recurring Basis [Member] | Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total	555,479	913,034
Recurring Basis [Member] | Level 1 [Member] | Cash [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents	138,791	405,648
Recurring Basis [Member] | Level 1 [Member] | Money Market Funds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents	416,688	507,386
Recurring Basis [Member] | Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total	1,665,782	1,466,095
Recurring Basis [Member] | Level 2 [Member] | Corporate Debt Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents	11,824
Marketable securities, fair value	1,150,184	1,168,766
Recurring Basis [Member] | Level 2 [Member] | Certificates of Deposit [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents	116,603
Marketable securities, fair value	57,631	45,164
Recurring Basis [Member] | Level 2 [Member] | Commercial Paper [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents		9,997
Marketable securities, fair value	304,620	212,719
Recurring Basis [Member] | Level 2 [Member] | US Treasury Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities, fair value	11,857	16,192
Recurring Basis [Member] | Level 2 [Member] | Government-sponsored Enterprise Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities, fair value	13,063	13,257
Recurring Basis [Member] | Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Other non-current assets	2,212	2,212
Total	$ 2,212	$ 2,212