Marketable Securities and Cash Equivalents - Summary of Marketable Securities and Cash Equivalents (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Marketable Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost		$ 51,208
Unrealized Losses		(9)
Fair Value		51,199
Corporate Debt Securities [Member] \| Marketable Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost		7,487
Unrealized Losses		(8)
Fair Value		7,479
Commercial Paper [Member] \| Marketable Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost		31,766
Fair Value		31,766
Government Securities [Member] \| Marketable Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost		11,955
Unrealized Losses		(1)
Fair Value		11,954
Cash Equivalents [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 16,705	18,290
Fair Value	16,705	18,290
Cash Equivalents [Member] \| Money Market Funds [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	16,705	16,292
Fair Value	$ 16,705	16,292
Cash Equivalents [Member] \| Commercial Paper [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost		1,998
Fair Value		$ 1,998

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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-Publisher FASB
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-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
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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).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
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-Publisher FASB
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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).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
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-URI http://asc.fasb.org/extlink&oid=118942338&loc=SL82898722-210454

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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