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Investments - Investments Classified as Short-Term Available-for-Sale Investments (Detail) - USD ($) $ in Thousands | Sep. 30, 2018 | Dec. 31, 2017
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Schedule of Available-for-sale Securities [Line Items] |  |
Fair value of available-for-sale investments | $ 219,776 | $ 209,434
Time Deposits and Certificates of Deposit [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Fair value of available-for-sale investments | 14,552 | 9,757
Bankers Acceptance Drafts [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Fair value of available-for-sale investments | 2,107 | 5,330
Asset-Backed Securities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Fair value of available-for-sale investments | 38,947 | 36,990
Commercial Paper [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Fair value of available-for-sale investments | 32,057 | 13,750
Corporate Obligations [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Fair value of available-for-sale investments | 71,971 | 77,821
Municipal Bonds [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Fair value of available-for-sale investments | 1,288 | 1,970
U.S. Treasury Obligations [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Fair value of available-for-sale investments | 28,208 | 28,078
U.S. Agency Obligations [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Fair value of available-for-sale investments | $ 30,646 | $ 35,738

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- Definition Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), classified as current. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=109979856&loc=d3e26626-111562 + Details
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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. + Details
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