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Investments - Gross Unrealized Gains and (Losses) Aggregated by Investment Category (Detail) - USD ($) $ in Thousands | Jun. 30, 2019 | Dec. 31, 2018
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Schedule of Available-for-sale Securities [Line Items] |  |
Investments, Cost | $ 93,350 | $ 73,994
Investments, Gross Unrealized Gains | 8 | 7
Investments, Gross Unrealized (Losses) | (373) | (175)
Investments, Estimated Fair Value | 92,985 | 73,826
Time Deposits and Certificates of Deposit [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Investments, Cost | 5,261 | 102
Investments, Gross Unrealized Gains | 1 |
Investments, Estimated Fair Value | 5,262 | 102
Bankers' Acceptance Drafts [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Investments, Cost | 3,833 | 989
Investments, Estimated Fair Value | 3,833 | 989
Asset-Backed Securities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Investments, Cost |  | 9,121
Investments, Gross Unrealized Gains |  | 1
Investments, Gross Unrealized (Losses) |  | (9)
Investments, Estimated Fair Value |  | 9,113
Commercial Paper [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Investments, Cost | 60,526 | 19,504
Investments, Gross Unrealized (Losses) | (372) | (145)
Investments, Estimated Fair Value | 60,154 | 19,359
Corporate Obligations [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Investments, Cost | 8,218 | 9,367
Investments, Gross Unrealized Gains | 1 |
Investments, Gross Unrealized (Losses) |  | (15)
Investments, Estimated Fair Value | 8,219 | 9,352
U.S. Treasury Obligations [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Investments, Cost |  | 13,294
Investments, Gross Unrealized Gains |  | 4
Investments, Estimated Fair Value |  | 13,298
U.S. Agency Obligations [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Investments, Cost | 15,512 | 21,617
Investments, Gross Unrealized Gains | 6 | 2
Investments, Gross Unrealized (Losses) | (1) | (6)
Investments, Estimated Fair Value | 15,517 | 21,613
Group Insurance Contracts [Member] | Long Term Investments [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Investments, Cost | 5,567 | 5,546
Investments, Gross Unrealized Gains | 434 | 344
Investments, Gross Unrealized (Losses) | 0 |
Investments, Estimated Fair Value | $ 6,001 | $ 5,890

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- Definition Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading. + References No definition available. + 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://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=118939692&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 No definition available. + Details
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- Definition This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any. + References No definition available. + Details
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