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Investments - Investments Classified as Short-Term Available-for-Sale Investments (Detail) - USD ($) $ in Thousands | Jun. 30, 2017 | Dec. 31, 2016
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Schedule of Available-for-sale Securities [Line Items] |  |
Fair value of available-for-sale investments | $ 149,016 | $ 189,463
Time Deposits and Certificates of Deposit [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Fair value of available-for-sale investments | 13,530 | 23,818
Bankers Acceptance Drafts [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Fair value of available-for-sale investments | 1,934 | 1,439
Asset-Backed Securities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Fair value of available-for-sale investments | 32,632 | 36,809
Commercial Paper [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Fair value of available-for-sale investments | 11,629 | 24,381
Corporate Obligations [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Fair value of available-for-sale investments | 46,990 | 46,707
Municipal Bonds [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Fair value of available-for-sale investments | 250 | 591
Promissory Note [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Fair value of available-for-sale investments | 675 | 675
U.S. Treasury Obligations [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Fair value of available-for-sale investments | 16,928 | 25,414
U.S. Agency Obligations [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Fair value of available-for-sale investments | $ 24,448 | $ 29,629

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