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Investments - Fair Value of Short-Term Available-for-Sale Investments (Detail) - Short-Term Investments [Member] - USD ($) $ in Thousands | Jun. 30, 2015 | Dec. 31, 2014
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Schedule of Investments [Line Items] |  |
Fair value of available-for-sale investments | $ 177,433 | $ 129,594
Time Deposits and Certificates of Deposit [Member] |  |
Schedule of Investments [Line Items] |  |
Fair value of available-for-sale investments | 23,630 | 20,900
Asset-Backed Securities [Member] |  |
Schedule of Investments [Line Items] |  |
Fair value of available-for-sale investments | 155 |
Bankers' Acceptance Drafts [Member] |  |
Schedule of Investments [Line Items] |  |
Fair value of available-for-sale investments | 222 | 82
Commercial Paper [Member] |  |
Schedule of Investments [Line Items] |  |
Fair value of available-for-sale investments | 3,450 |
Corporate Obligations [Member] |  |
Schedule of Investments [Line Items] |  |
Fair value of available-for-sale investments | 59,719 | 24,020
Municipal Bonds [Member] |  |
Schedule of Investments [Line Items] |  |
Fair value of available-for-sale investments | 7,057 | 2,099
U.S. Agency Obligations [Member] |  |
Schedule of Investments [Line Items] |  |
Fair value of available-for-sale investments | $ 83,200 | $ 82,493

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- Definition Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 25 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=51813488&loc=d3e22054-111558 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 5 -Subparagraph (aa) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=49167202&loc=d3e26610-111562 + Details
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