Marketable Securities - Summary of Fair Value of Available-for-Sale Marketable Securities by Type of Security (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 54,345	$ 171,632
Gross Unrealized Gains	62	20
Gross Unrealized Losses		(97)
Fair Value	54,407	171,555
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	6,189	36,723
Fair Value	6,189	36,723
U.S. Government Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	29,950	39,910
Gross Unrealized Gains	24
Gross Unrealized Losses		(12)
Fair Value	29,974	39,898
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	18,206	94,999
Gross Unrealized Gains	38	20
Gross Unrealized Losses		(85)
Fair Value	$ 18,244	$ 94,934

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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