Fair Value Measurements - Summary of Fair Value of Financial Instruments (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Short-term investments:
Short-term investments	$ 87,102	$ 72,192
U.S. Government Securities [Member]
Short-term investments:
Short-term investments	11,985	11,885
Asset Backed Securities [Member]
Short-term investments:
Short-term investments	9,480	8,383
Corporate Securities [Member]
Short-term investments:
Short-term investments	19,080	22,082
Commercial Paper [Member]
Short-term investments:
Short-term investments	46,557	29,842
Fair Value, Measurements, Recurring [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| U.S, Treasury Money Market Funds [Member]
Cash equivalents:
Cash equivalents	15,496	4,540
Fair Value, Measurements, Recurring [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| U.S. Government Securities [Member]
Short-term investments:
Short-term investments	11,985	11,885
Fair Value, Measurements, Recurring [Member] \| Significant Other Observable Inputs (Level 2) [Member]
Other assets:
Foreign exchange derivatives not designated as hedging instruments	4	40
Fair Value, Measurements, Recurring [Member] \| Significant Other Observable Inputs (Level 2) [Member] \| Asset Backed Securities [Member]
Short-term investments:
Short-term investments	9,480	8,383
Fair Value, Measurements, Recurring [Member] \| Significant Other Observable Inputs (Level 2) [Member] \| Corporate Securities [Member]
Short-term investments:
Short-term investments	19,080	22,082
Fair Value, Measurements, Recurring [Member] \| Significant Other Observable Inputs (Level 2) [Member] \| Commercial Paper [Member]
Cash equivalents:
Cash equivalents	5,817	1,029
Short-term investments:
Short-term investments	46,557	29,842
Fair Value, Measurements, Recurring [Member] \| Significant Other Observable Inputs (Level 2) [Member] \| Repurchase Agreements [Member]
Cash equivalents:
Cash equivalents		2,500
Fair Value, Measurements, Recurring [Member] \| Significant Unobservable Inputs (Level 3) [Member]
Liabilities:
Contingent consideration	$ 12,079	$ 11,948

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Other assets fair value disclosure.

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

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Fair value of contingent consideration in a business combination that is classified in shareholders' equity.

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Fair value as of the balance sheet date of all foreign currency derivative assets not designated as hedging instruments.

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