Debt (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Unamortized debt issuance expense	$ 0.7	$ 0.6
Long-term debt, excluding current portion	$ 255.0	196.0
Senior A Notes Due 2022 [Member]
Debt Instrument [Line Items]
Debt instrument, stated interest rate	3.67%
Senior B Notes Due 2024 [Member]
Debt Instrument [Line Items]
Debt instrument, stated interest rate	3.82%
Senior C Notes Due 2027 [Member]
Debt Instrument [Line Items]
Debt instrument, stated interest rate	4.02%
Note Payable Due 2019 [Member]
Debt Instrument [Line Items]
Long-term debt, gross		0.1
Revolving credit facility, due 2020 [Member]
Debt Instrument [Line Items]
Long-term debt, gross		28.6
Senior Notes [Member] \| Senior A Notes Due 2022 [Member]
Debt Instrument [Line Items]
Debt instrument, stated interest rate	3.67%
Long-term debt, gross		42.0
Senior Notes [Member] \| Senior B Notes Due 2024 [Member]
Debt Instrument [Line Items]
Long-term debt	$ 53.0
Debt instrument, stated interest rate	3.82%
Long-term debt, gross		53.0
Senior Notes [Member] \| Senior C Notes Due 2027 [Member]
Debt Instrument [Line Items]
Long-term debt	$ 73.0
Debt instrument, stated interest rate	4.02%
Long-term debt, gross		$ 73.0
Term Loan Due 2024 [Domain]
Debt Instrument [Line Items]
Long-term debt	$ 90.0
Senior A Notes Due 2022 [Member]
Debt Instrument [Line Items]
Long-term debt	42.0
Term Loan Due 2024 [Member]
Debt Instrument [Line Items]
Long-term debt, excluding current portion	$ 87.7
Debt instrument, stated interest rate	2.78%
Long-term debt, gross	$ 90.0

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.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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-SubTopic 20
-Section 50
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Contractual interest rate for funds borrowed, under the debt agreement.

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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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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.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
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- Definition

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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- Definition

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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