Short-term Investments - Summary of Major Security and Type of Investments (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 79,490	$ 86,559
Gross Unrealized Gains	20
Gross Unrealized Losses	(2)	(30)
Fair Value	79,508	86,529
U.S. Government Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	6,974	15,967
Gross Unrealized Gains	3
Gross Unrealized Losses		(2)
Fair Value	6,977	15,965
Asset Backed Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	6,235	8,595
Gross Unrealized Gains	3
Gross Unrealized Losses		(7)
Fair Value	6,238	8,588
Corporate Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	36,065	19,975
Gross Unrealized Gains	14
Gross Unrealized Losses	(2)	(21)
Fair Value	36,077	19,954
Commercial Paper [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	30,216	42,022
Fair Value	$ 30,216	$ 42,022

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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- Definition

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

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)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

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- Definition

Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

No definition available.

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- Definition

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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