Fair Value Measurements and Marketable Securities - Summary of Gross Unrealized Gains and Losses of Marketable Securities (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 32,269	$ 81,391
Gross Unrealized Gains	6
Gross Unrealized Losses		(28)
Fair Value	32,275	81,363
U.S. Government Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	13,468	37,819
Gross Unrealized Gains	5
Gross Unrealized Losses		(4)
Fair Value	13,473	37,815
U.S. Corporate Bonds [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	4,019	26,696
Gross Unrealized Gains	1
Gross Unrealized Losses		(24)
Fair Value	4,020	26,672
Commercial Paper [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	14,782	16,876
Fair Value	$ 14,782	$ 16,876

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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-Section 50
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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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-Publisher FASB
-Name Accounting Standards Codification
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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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-Publisher FASB
-Name Accounting Standards Codification
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