Debt and Financing Obligations (Schedule of Debt) (Details) - USD ($)	Dec. 31, 2022	Dec. 31, 2021
Debt Instrument [Line Items]
Total borrowings	$ 543,800,000	$ 627,000,000.0
Debt issuance costs	(11,600,000)	(13,400,000)
Total debt and financing obligation	532,200,000	613,600,000
Less: current portion of long-term debt and financing obligation	3,300,000	3,200,000
Total long-term debt and financing obligation	$ 528,900,000	610,400,000
Senior Notes, Due 2029 \| Senior notes
Debt Instrument [Line Items]
Interest rate on senior notes (as a percent)	4.875%
Total borrowings	$ 500,000,000.0	500,000,000.0
$350.0 revolving credit facility, due 2026 ("Revolving Facility") \| Line of Credit \| Revolving credit facility
Debt Instrument [Line Items]
Principal amount of term loan	350,000,000.0
Total borrowings	$ 35,000,000.0	115,000,000.0
5.346 percent financing obligation, due 2024 \| Financing Obligation
Debt Instrument [Line Items]
Interest rate on senior notes (as a percent)	5.346%
Total borrowings	$ 8,800,000	$ 12,000,000.0

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.

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Contractual interest rate for funds borrowed, under the debt agreement.

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Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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Amount, excluding unamortized premium (discount) and debt issuance cost, of long-term debt. Excludes lease obligation.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt, classified as current. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Amount, excluding unamortized premium (discount) and debt issuance cost, of long-term debt classified as noncurrent. Excludes lease obligation.

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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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