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Investments - Gross Unrealized Gains and (Losses) Aggregated by Investment Category (Detail) - USD ($) $ in Thousands | Dec. 31, 2016 | Dec. 31, 2015
--- | --- | ---
Schedule of Available-for-sale Securities [Line Items] |  |
Investments, Cost | $ 189,538 | $ 431,382
Investments, Gross Unrealized Gains | 35 | 21
Investments, Gross Unrealized (Losses) | (110) | (740)
Investments, Estimated Fair Value | 189,463 | 430,663
Long Term Investments [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Investments, Cost | 10,576 |
Investments, Gross Unrealized (Losses) | (718) |
Investments, Estimated Fair Value | 9,858 |
Time Deposits and Certificates of Deposit [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Investments, Cost | 23,818 | 11,893
Investments, Gross Unrealized (Losses) |  | (1)
Investments, Estimated Fair Value | 23,818 | 11,892
Bankers Acceptance Drafts [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Investments, Cost | 1,439 | 728
Investments, Estimated Fair Value | 1,439 | 728
Asset-Backed Securities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Investments, Cost | 36,847 | 125,271
Investments, Gross Unrealized Gains | 6 |
Investments, Gross Unrealized (Losses) | (44) | (274)
Investments, Estimated Fair Value | 36,809 | 124,997
Commercial Paper [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Investments, Cost | 24,423 |
Investments, Gross Unrealized (Losses) | (42) |
Investments, Estimated Fair Value | 24,381 |
Corporate Obligations [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Investments, Cost | 46,700 | 165,445
Investments, Gross Unrealized Gains | 21 | 5
Investments, Gross Unrealized (Losses) | (14) | (341)
Investments, Estimated Fair Value | 46,707 | 165,109
Municipal Bonds [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Investments, Cost | 591 | 8,346
Investments, Gross Unrealized Gains |  | 13
Investments, Gross Unrealized (Losses) |  | (4)
Investments, Estimated Fair Value | 591 | 8,355
Promissory Note [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Investments, Cost | 675 |
Investments, Estimated Fair Value | 675 |
U.S. Treasury Obligations [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Investments, Cost | 25,414 |
Investments, Estimated Fair Value | 25,414 |
U.S. Agency Obligations [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Investments, Cost | 29,631 | 119,699
Investments, Gross Unrealized Gains | 8 | 3
Investments, Gross Unrealized (Losses) | (10) | (120)
Investments, Estimated Fair Value | 29,629 | $ 119,582
Group Insurance Contracts [Member] | Long Term Investments [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Investments, Cost | 6,276 |
Investments, Gross Unrealized (Losses) | (718) |
Investments, Estimated Fair Value | 5,558 |
Minority Interest in Private Company [Member] | Long Term Investments [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Investments, Cost | 4,300 |
Investments, Estimated Fair Value | $ 4,300 |

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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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- Definition Amount before tax of unrealized loss 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 (c) -URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27161-111563 + Details
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