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Fair Value of Marketable Securities (Detail) - USD ($) $ in Millions | Sep. 30, 2022 | Dec. 31, 2021 | Sep. 30, 2021
--- | --- | --- | ---
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |  |
Trading Securities | $ 5.6 | $ 5.7 | $ 5.6
Deferred Compensation Plan [Member] |  |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |  |
Trading Securities | 0.6 | 0.6 | 0.5
Fair Value, Inputs, Level 1 |  |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |  |
Trading Securities | 5.6 | 5.7 | 5.6
Fair Value, Inputs, Level 1 | Deferred Compensation Plan [Member] |  |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |  |
Trading Securities | 0.6 | 0.6 | 0.5
Fair Value, Inputs, Level 1 | Equity Funds | Deferred Compensation Plan [Member] |  |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |  |
Trading Securities | 0.5 | 0.2 | 0.1
Fair Value, Inputs, Level 1 | Money Market Funds |  |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |  |
Trading Securities | 5.6 | 5.7 | 5.6
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 | $ 0.4 | $ 0.4

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