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Fair Value of Marketable Securities (Detail) - USD ($) $ in Millions | Sep. 30, 2019 | Dec. 31, 2018 | Sep. 30, 2018
--- | --- | --- | ---
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |  |
Trading Securities | $ 5.9 | $ 4.8 | $ 5.3
Deferred Compensation Plan [Member] |  |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |  |
Trading Securities | 0.1 | 0.0 | 0.0
Fair Value, Inputs, Level 1 |  |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |  |
Trading Securities | 5.9 | 4.8 | 5.3
Fair Value, Inputs, Level 1 | Deferred Compensation Plan [Member] |  |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |  |
Trading Securities | 0.1 |  |
Fair Value, Inputs, Level 1 | Equity Funds |  |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |  |
Trading Securities |  |  | 3.0
Fair Value, Inputs, Level 1 | Fixed Income Funds |  |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |  |
Trading Securities |  |  | $ 2.3
Fair Value, Inputs, Level 1 | Money Market Funds |  |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |  |
Trading Securities | 5.9 | $ 4.8 |
Fair Value, Inputs, Level 1 | Money Market Funds | Deferred Compensation Plan [Member] |  |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |  |
Trading Securities | $ 0.1 |  |

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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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- Definition Amount of investment in debt security measured at fair value with change in fair value recognized in net income (trading) and investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.4) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 + Details
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