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Cash, Cash Equivalents and Investments - Gross Unrealized Losses and Fair Value for Available-for-Sale Investments (Detail) $ in Thousands | Dec. 31, 2018 USD ($)
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Debt Securities, Available-for-sale [Line Items] |
Fair Value, Less than 12 months | $ 318,908
Unrealized Losses, Less than 12 months | (1,445)
Fair Value, Greater than 12 Months | 163,775
Unrealized Losses, Greater than 12 Months | (810)
Fair Value | 482,683
Unrealized Losses | (2,255)
Corporate Bonds [Member] |
Debt Securities, Available-for-sale [Line Items] |
Fair Value, Less than 12 months | 145,596
Unrealized Losses, Less than 12 months | (1,268)
Fair Value, Greater than 12 Months | 99,886
Unrealized Losses, Greater than 12 Months | (495)
Fair Value | 245,482
Unrealized Losses | (1,763)
Treasury Bills [Member] |
Debt Securities, Available-for-sale [Line Items] |
Fair Value, Less than 12 months | 114,836
Unrealized Losses, Less than 12 months | (73)
Fair Value, Greater than 12 Months | 13,850
Unrealized Losses, Greater than 12 Months | (13)
Fair Value | 128,686
Unrealized Losses | (86)
Asset-Backed Securities [Member] |
Debt Securities, Available-for-sale [Line Items] |
Fair Value, Less than 12 months | 47,762
Unrealized Losses, Less than 12 months | (91)
Fair Value, Greater than 12 Months | 44,585
Unrealized Losses, Greater than 12 Months | (262)
Fair Value | 92,347
Unrealized Losses | (353)
Sovereign Bonds [Member] |
Debt Securities, Available-for-sale [Line Items] |
Fair Value, Less than 12 months | 3,492
Unrealized Losses, Less than 12 months | (4)
Fair Value, Greater than 12 Months | 4,609
Unrealized Losses, Greater than 12 Months | (30)
Fair Value | 8,101
Unrealized Losses | (34)
Agency Bonds [Member] |
Debt Securities, Available-for-sale [Line Items] |
Fair Value, Less than 12 months | 5,920
Unrealized Losses, Less than 12 months | (9)
Fair Value, Greater than 12 Months | 0
Unrealized Losses, Greater than 12 Months | 0
Fair Value | 5,920
Unrealized Losses | (9)
Municipal Bonds [Member] |
Debt Securities, Available-for-sale [Line Items] |
Fair Value, Less than 12 months | 1,302
Unrealized Losses, Less than 12 months | 0
Fair Value, Greater than 12 Months | 845
Unrealized Losses, Greater than 12 Months | (10)
Fair Value | 2,147
Unrealized Losses | $ (10)

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- Definition Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for twelve months or longer. + References No definition available. + Details
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- Definition Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale in a continuous loss position. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27337-111563 + Details
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- Definition Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for less than twelve months. + References No definition available. + Details
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