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Fair Value of Marketable Securities (Detail) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022	Sep. 30, 2022
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Trading Securities	$ 5.9	$ 5.8	$ 5.6
Deferred Compensation Plan [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Trading Securities	1.1	0.6	0.6
Fair Value, Inputs, Level 1
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Trading Securities	5.9	5.8	5.6
Fair Value, Inputs, Level 1 | Deferred Compensation Plan [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Trading Securities	1.1	0.6	0.6
Fair Value, Inputs, Level 1 | Equity Funds | Deferred Compensation Plan [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Trading Securities	1.0	0.5	0.5
Fair Value, Inputs, Level 1 | Money Market Funds
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Trading Securities	5.9	5.8	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	$ 0.1	$ 0.1

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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://www.xbrl.org/2003/role/disclosureRef
-Topic 210
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(2))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480566/210-10-S99-1

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-Topic 210
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-Topic 942
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-Section S99
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-Publisher FASB
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