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Investments - Gross Unrealized Gains and (Losses) Aggregated by Investment Category Short-Term and Long-Term Securities (Detail) - USD ($) $ in Thousands | Sep. 30, 2016 | Dec. 31, 2015
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Schedule of Available-for-sale Securities [Line Items] |  |
Investments, Cost | $ 53,088 | $ 431,382
Investments, Gross Unrealized Gains | 34 | 21
Investments, Gross Unrealized (Losses) | (18) | (740)
Investments, Estimated Fair Value | 53,104 | 430,663
Time Deposits and Certificates of Deposit [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Investments, Cost | 1,395 | 11,893
Investments, Gross Unrealized (Losses) |  | (1)
Investments, Estimated Fair Value | 1,395 | 11,892
Bankers' Acceptance Drafts [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Investments, Cost | 2,487 | 728
Investments, Estimated Fair Value | 2,487 | 728
Asset-Backed Securities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Investments, Cost | 18,317 | 125,271
Investments, Gross Unrealized Gains | 13 |
Investments, Gross Unrealized (Losses) | (4) | (274)
Investments, Estimated Fair Value | 18,326 | 124,997
Commercial Paper [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Investments, Cost | 2,794 |
Investments, Gross Unrealized (Losses) | (1) |
Investments, Estimated Fair Value | 2,793 |
Corporate Obligations [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Investments, Cost | 16,699 | 165,445
Investments, Gross Unrealized Gains | 15 | 5
Investments, Gross Unrealized (Losses) | (13) | (341)
Investments, Estimated Fair Value | 16,701 | 165,109
Municipal Bonds [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Investments, Cost | 592 | 8,346
Investments, Gross Unrealized Gains | 1 | 13
Investments, Gross Unrealized (Losses) |  | (4)
Investments, Estimated Fair Value | 593 | 8,355
U.S. Treasury Obligations [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Investments, Cost | 1,151 |
Investments, Gross Unrealized Gains | 1 |
Investments, Estimated Fair Value | 1,152 |
U.S. Agency Obligations [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Investments, Cost | 9,653 | 119,699
Investments, Gross Unrealized Gains | 4 | 3
Investments, Gross Unrealized (Losses) |  | (120)
Investments, Estimated Fair Value | 9,657 | $ 119,582
Group Insurance Contracts [Member] | Long Term Investments [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Investments, Cost | 5,988 |
Investments, Gross Unrealized (Losses) | (32) |
Investments, Estimated Fair Value | $ 5,956 |

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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=65884222&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=73527792&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=66010992&loc=d3e26610-111562 + Details
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- Definition Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27161-111563 + Details
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