Debt - Schedule of Debt Obligations (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Total debt excluding financing lease liabilities	$ 664.7
Financing lease liabilities (Please refer to Note 16)	8.8	$ 12.4
Total debt	673.5	683.9
Less unamortized discount on Term Debt	1.2	1.4
Less unamortized debt issuance costs on Term Debt	4.5	5.4
Less current portion of long-term debt	7.2	10.8
Long-term debt, less current portion	660.6	666.3
Term Debt [Member]
Debt Instrument [Line Items]
Total debt excluding financing lease liabilities	$ 664.7	$ 671.5

Debt instrument carrying amount and finance lease liability.

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- Definition

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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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.

+ References

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Amount, after accumulated amortization, of debt discount.

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- Definition

Present value of lessee's discounted obligation for lease payments from finance lease.

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Amount of long-term debt and lease obligation, classified as noncurrent.

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Amount of long-term debt and lease obligation, classified as current.

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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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