Marketable Securities - Summary of Available -for-sale Marketable Securities (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Marketable Securities [Line Items]
Amortized Cost	$ 459,272	$ 437,350
Gross Unrealized Gains	58	23
Gross Unrealized Losses	(70)	(22)
Estimated Fair Value	459,260	437,351
U.S. Treasury and Other Government Securities [Member]
Marketable Securities [Line Items]
Amortized Cost	204,473	245,666
Gross Unrealized Gains	49	13
Gross Unrealized Losses	(4)	(11)
Estimated Fair Value	204,518	245,668
Financial Institution Debt Securities [Member]
Marketable Securities [Line Items]
Amortized Cost	169,979	138,445
Gross Unrealized Gains	7	6
Gross Unrealized Losses	(45)	(8)
Estimated Fair Value	169,941	138,443
Corporate Debt Securities [Member]
Marketable Securities [Line Items]
Amortized Cost	51,311	41,765
Gross Unrealized Gains	1	3
Gross Unrealized Losses	(13)	(2)
Estimated Fair Value	51,299	41,766
Other Asset Backed Securities [Member]
Marketable Securities [Line Items]
Amortized Cost	33,509	11,474
Gross Unrealized Gains	1	1
Gross Unrealized Losses	(8)	(1)
Estimated Fair Value	$ 33,502	$ 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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