Fair Value of Financial Instruments - Schedule of Company's Classified Assets Measured at Fair Value on Recurring Basis (Detail) - Recurring - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Fair Value Asset Measured On Recurring Basis [Line Items]
Total assets	$ 127,895	$ 111,742
Money market funds
Fair Value Asset Measured On Recurring Basis [Line Items]
Cash and Cash Equivalents	16,691	265
Corporate debt securities
Fair Value Asset Measured On Recurring Basis [Line Items]
Short-term investments	56,603	50,052
Long-term investments	17,388
Commercial paper
Fair Value Asset Measured On Recurring Basis [Line Items]
Short-term investments	36,205	57,453
U.S. Government Agency Securities and Treasuries
Fair Value Asset Measured On Recurring Basis [Line Items]
Long-term investments	1,008
U.S. Government Agency Securities and Treasuries
Fair Value Asset Measured On Recurring Basis [Line Items]
Short-term investments		3,972
Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value Asset Measured On Recurring Basis [Line Items]
Total assets	16,691	2,252
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Money market funds
Fair Value Asset Measured On Recurring Basis [Line Items]
Cash and Cash Equivalents	16,691	265
Quoted Prices in Active Markets for Identical Assets (Level 1) \| U.S. Government Agency Securities and Treasuries
Fair Value Asset Measured On Recurring Basis [Line Items]
Short-term investments		1,987
Significant Other Observable Inputs (Level 2)
Fair Value Asset Measured On Recurring Basis [Line Items]
Total assets	111,204	109,490
Significant Other Observable Inputs (Level 2) \| Corporate debt securities
Fair Value Asset Measured On Recurring Basis [Line Items]
Short-term investments	56,603	50,052
Long-term investments	17,388
Significant Other Observable Inputs (Level 2) \| Commercial paper
Fair Value Asset Measured On Recurring Basis [Line Items]
Short-term investments	36,205	57,453
Significant Other Observable Inputs (Level 2) \| U.S. Government Agency Securities and Treasuries
Fair Value Asset Measured On Recurring Basis [Line Items]
Long-term investments	1,008
Significant Other Observable Inputs (Level 2) \| U.S. Government Agency Securities and Treasuries
Fair Value Asset Measured On Recurring Basis [Line Items]
Short-term investments		1,985
Significant Unobservable Inputs (Level 3)
Fair Value Asset Measured On Recurring Basis [Line Items]
Total assets	0	0
Significant Unobservable Inputs (Level 3) \| Money market funds
Fair Value Asset Measured On Recurring Basis [Line Items]
Cash and Cash Equivalents	0	0
Significant Unobservable Inputs (Level 3) \| Corporate debt securities
Fair Value Asset Measured On Recurring Basis [Line Items]
Short-term investments	0	0
Long-term investments	0
Significant Unobservable Inputs (Level 3) \| Commercial paper
Fair Value Asset Measured On Recurring Basis [Line Items]
Short-term investments	0	0
Significant Unobservable Inputs (Level 3) \| U.S. Government Agency Securities and Treasuries
Fair Value Asset Measured On Recurring Basis [Line Items]
Long-term investments	$ 0
Significant Unobservable Inputs (Level 3) \| U.S. Government Agency Securities and Treasuries
Fair Value Asset Measured On Recurring Basis [Line Items]
Short-term investments		$ 0

Fair Value Asset Measured On Recurring Basis [Line Items]

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Long term investments fair value disclosure.

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- Definition

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

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Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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- Definition

Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

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