Fair Value Measurements - Summary of Gross Unrealized Gains and Losses of Marketable Securities (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 1,105,003	$ 438,052
Gross Unrealized Gains	222	451
Gross Unrealized Losses	(458)	(36)
Fair Value	1,104,767	438,467
U.S. Government Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	173,073	160,589
Gross Unrealized Gains	30	11
Gross Unrealized Losses	(6)	(12)
Fair Value	173,097	160,588
U.S. Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	346,021	122,882
Gross Unrealized Gains	118	240
Gross Unrealized Losses	(282)	(15)
Fair Value	345,857	123,107
International Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	202,848	57,485
Gross Unrealized Gains	70	200
Gross Unrealized Losses	(148)	(9)
Fair Value	202,770	57,676
U.S. Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	170,803	45,963
Gross Unrealized Gains	4
Gross Unrealized Losses	(11)
Fair Value	170,796	45,963
International Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	212,258	51,133
Gross Unrealized Losses	(11)
Fair Value	$ 212,247	$ 51,133

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), classified as current.

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