Marketable Securities - Summary of Available-for-Sale Short-Term and Long-Term Investments (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Short-term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 46,682	$ 36,230
Gross Unrealized Gains	17	2
Gross Unrealized Losses	(5)
Aggregate Fair Value	46,694	36,232
Long-term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	5,968
Gross Unrealized Gains	4
Aggregate Fair Value	5,972
Corporate Debt Securities [Member] \| Short-term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	43,681	36,230
Gross Unrealized Gains	17	2
Gross Unrealized Losses	(5)
Aggregate Fair Value	43,693	$ 36,232
Corporate Debt Securities [Member] \| Long-term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	5,968
Gross Unrealized Gains	4
Aggregate Fair Value	5,972
U.S. Goverment and Goverment Agency Debt Securities [Member] \| Short-term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	3,001
Aggregate Fair Value	$ 3,001

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).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
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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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-Publisher FASB
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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

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
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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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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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