Marketable Securities and Cash Equivalents - Summary of Marketable Securities and Cash Equivalents (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 54,364
Fair Value	54,364
Cash Equivalents [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	32,440	$ 18,290
Fair Value	32,440	18,290
Cash Equivalents [Member] \| Money Market Funds [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	32,440	16,292
Fair Value	32,440	16,292
Cash Equivalents [Member] \| Commercial Paper [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost		1,998
Fair Value		1,998
Marketable Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	21,924	51,208
Unrealized Losses		(9)
Fair Value	21,924	51,199
Marketable Securities [Member] \| Corporate Debt Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	1,997	7,487
Unrealized Losses		(8)
Fair Value	1,997	7,479
Marketable Securities [Member] \| Commercial Paper [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	16,930	31,766
Fair Value	16,930	31,766
Marketable Securities [Member] \| Government Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	2,997	11,955
Unrealized Losses		(1)
Fair Value	$ 2,997	$ 11,954

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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-Topic 320
-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
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
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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 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
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