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Investments - Gross Unrealized Gains and (Losses) Aggregated by Investment Category (Detail) - USD ($) $ in Millions | Dec. 31, 2020 | Dec. 31, 2019
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Schedule of Available-for-sale Securities [Line Items] |  |
Investments, Cost | $ 227.7 | $ 109.7
Investments, Gross Unrealized (Losses) |  | (0.3)
Investments, Estimated Fair Value | 227.7 | 109.4
Time Deposits and Certificates of Deposit [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Investments, Cost | 0.7 | 13.1
Investments, Estimated Fair Value | 0.7 | 13.1
Bankers' Acceptance Drafts [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Investments, Cost | 3.8 | 4.0
Investments, Estimated Fair Value | 3.8 | 4.0
U.S. Treasury Obligations [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Investments, Cost | 223.2 | 5.0
Investments, Estimated Fair Value | 223.2 | 5.0
Group Insurance Contracts [Member] | Long Term Investments [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Investments, Cost | 5.6 | 5.2
Investments, Gross Unrealized Gains | 0.9 | 0.6
Investments, Estimated Fair Value | $ 6.5 | 5.8
Commercial Paper [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Investments, Cost |  | 61.5
Investments, Gross Unrealized (Losses) |  | (0.3)
Investments, Estimated Fair Value |  | 61.2
U.S. Agency Obligations [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Investments, Cost |  | 26.1
Investments, Estimated Fair Value |  | $ 26.1

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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=121645371&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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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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