Short-term Investments - Summary of Debt Securities by Major Security Type (Detail) $ in Thousands	Sep. 30, 2019 USD ($)
Schedule Of Available For Sale Securities [Line Items]
Amortized cost	$ 25,926
Gross unrealized gains	51
Gross unrealized losses	(13)
Fair value	25,964
U.S. Government Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized cost	19,927
Gross unrealized gains	46
Gross unrealized losses	(9)
Fair value	19,964
U.S. T-bills [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized cost	4,999
Gross unrealized gains	3
Gross unrealized losses	(2)
Fair value	5,000
U.S. Agency Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized cost	1,000
Gross unrealized gains	2
Gross unrealized losses	(2)
Fair value	$ 1,000

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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