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Investments - Investments Classified as Short-Term Available-for-Sale Investments (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Fair value of available-for-sale investments	$ 203,686	$ 209,434
Time Deposits and Certificates of Deposit [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair value of available-for-sale investments	18,455	9,757
Bankers Acceptance Drafts [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair value of available-for-sale investments	2,522	5,330
Asset-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair value of available-for-sale investments	34,727	36,990
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair value of available-for-sale investments	25,925	13,750
Corporate Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair value of available-for-sale investments	66,663	77,821
Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair value of available-for-sale investments	2,615	1,970
U.S. Treasury Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair value of available-for-sale investments	31,434	28,078
U.S. Agency Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair value of available-for-sale investments	$ 21,345	$ 35,738

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- Definition

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

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No definition available.

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- Definition

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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