Marketable Securities - Summary of Available -for-sale Marketable Securities (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Marketable Securities [Line Items]
Amortized Cost	$ 814,155	$ 437,350
Gross Unrealized Gains	22	23
Gross Unrealized Losses	(195)	(22)
Estimated Fair Value	813,982	437,351
U.S. Treasury and Other Government Securities [Member]
Marketable Securities [Line Items]
Amortized Cost	251,302	245,666
Gross Unrealized Gains	9	13
Gross Unrealized Losses	(69)	(11)
Estimated Fair Value	251,242	245,668
Financial Institution Debt Securities [Member]
Marketable Securities [Line Items]
Amortized Cost	395,052	138,445
Gross Unrealized Gains	12	6
Gross Unrealized Losses	(66)	(8)
Estimated Fair Value	394,998	138,443
Corporate Debt Securities [Member]
Marketable Securities [Line Items]
Amortized Cost	32,099	41,765
Gross Unrealized Gains	0	3
Gross Unrealized Losses	(9)	(2)
Estimated Fair Value	32,090	41,766
Other Asset Backed Securities [Member]
Marketable Securities [Line Items]
Amortized Cost	135,702	11,474
Gross Unrealized Gains	1	1
Gross Unrealized Losses	(51)	(1)
Estimated Fair Value	$ 135,652	$ 11,474

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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