Total Debt - Schedule of Total Debt Outstanding (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Outstanding Principal	$ 1,637.7	$ 1,492.0
Issuance Costs and Fees	15.4	18.1
Long-Term Debt, Net	1,622.3	1,473.9
Current maturities of long-term debt	4.0	4.0
Total principal amount of debt, net of current maturities	1,633.7	1,488.0
Total debt, net of current maturities	1,618.3	1,469.9
Revolver \| Line of Credit
Debt Instrument [Line Items]
Issuance Costs and Fees	0.0
Long-Term Debt, Net	149.7
Revolver \| Line of Credit \| Carrying Amount
Debt Instrument [Line Items]
Long-Term Debt, Net	149.7
2027 Senior Notes \| Senior Notes
Debt Instrument [Line Items]
Outstanding Principal		600.0
Issuance Costs and Fees	6.8	8.0
Long-Term Debt, Net	593.2	592.0
2027 Senior Notes \| Senior Notes \| Carrying Amount
Debt Instrument [Line Items]
Fair value disclosure of debt	600.0
Long-Term Debt, Net	593.2	592.0
2028 Senior Notes \| Senior Notes
Debt Instrument [Line Items]
Outstanding Principal		500.0
Issuance Costs and Fees	5.4	6.1
Long-Term Debt, Net	494.6	493.9
2028 Senior Notes \| Senior Notes \| Carrying Amount
Debt Instrument [Line Items]
Fair value disclosure of debt	500.0
Long-Term Debt, Net	494.6	493.9
Term Loan \| Term Loan B due 2024 \| Line of Credit
Debt Instrument [Line Items]
Outstanding Principal		392.0
Issuance Costs and Fees	3.2	4.0
Long-Term Debt, Net	384.8	$ 388.0
Term Loan \| Term Loan B due 2024 \| Line of Credit \| Carrying Amount
Debt Instrument [Line Items]
Fair value disclosure of debt	$ 388.0

Long-term Debt, Excluding Current Maturities, Gross

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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

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Fair value portion of debt instrument payable, including, but not limited to, notes payable and loans payable.

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No definition available.

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

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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 after unamortized (discount) premium and debt issuance costs of long-term debt classified as noncurrent and excluding amounts to be repaid within one year or the normal operating cycle, if longer. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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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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