Marketable Securities - Summary of Available-for-Sale Debt Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Marketable Securities [Line Items]
Amortized Cost	$ 426,880	$ 15,936
Unrealized Gains		6
Unrealized Losses	(170)
Fair Value	426,710	15,942
U.S. Treasury Securities
Marketable Securities [Line Items]
Amortized Cost	346,066	15,936
Unrealized Gains		6
Unrealized Losses	(84)
Fair Value	345,982	$ 15,942
Corporate Securities
Marketable Securities [Line Items]
Amortized Cost	80,814
Unrealized Losses	(86)
Fair Value	$ 80,728

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).

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