Investments - Schedule of Investments by Security Type (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 112,984	$ 29,689
Gross Unrealized Gain	4	3
Gross Unrealized Loss	(2)	(2)
Fair Value	112,986	29,690
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	6,245	11,957
Fair Value	6,245	11,957
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,021	17,732
Gross Unrealized Gain		3
Gross Unrealized Loss		(2)
Fair Value	2,021	$ 17,733
Government Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	104,718
Gross Unrealized Gain	4
Gross Unrealized Loss	(2)
Fair Value	$ 104,720

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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