Fair Value Measurements Fair Value Inputs, Liabilities, Quantitative Information (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Fair Value Disclosures [Abstract]
Long-term Debt, Fair Value	$ 1,100.0
Unamortized Debt Issuance Expense	(7.4)	$ (8.5)
Business Combination, Contingent Consideration, Liability, Noncurrent	5.0
Long-term Debt, Gross	1,040.8	1,040.8
Fair Value, Inputs, Level 1 [Member]
Fair Value Disclosures [Abstract]
Deferred Compensation Plan Assets	14.4	11.8
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Deferred Compensation Plan Assets	$ 14.4	$ 11.8

Amount of liability recognized arising from contingent consideration in a business combination, expected to be settled beyond one year or the normal operating cycle, if longer.

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Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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Carrying amount as of the balance sheet date of assets held under deferred compensation agreements.

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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.

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The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

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The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of the respective bond issues. This does not include the amounts capitalized as part of the cost of the utility plant or asset.

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