Recurring Fair Value Measurement (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Derivatives, Fair Value [Line Items]
Prepayments	$ 4.3	$ 3.3
Fair Value Measured on a Recurring Basis
Derivatives, Fair Value [Line Items]
Prepayments	4.3	3.3
Fair Value Measured on a Recurring Basis \| Other Current Assets \| Other Derivative Instruments \| Natural Gas Commodity Contract
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross	0.5	0.2
Netting	0.0	0.0
Derivative Asset, Net	0.5	0.2
Fair Value Measured on a Recurring Basis \| Other Current Assets \| Other Derivative Instruments \| Natural Gas Commodity Contract \| Level 1
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross	0.0	0.0
Fair Value Measured on a Recurring Basis \| Other Current Assets \| Other Derivative Instruments \| Natural Gas Commodity Contract \| Level 2
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross	0.5	0.2
Fair Value Measured on a Recurring Basis \| Other Current Assets \| Other Derivative Instruments \| Natural Gas Commodity Contract \| Level 3
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross	$ 0.0	$ 0.0

Fair value of liability associated with financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, and obligation to return cash collateral under master netting arrangements.

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Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

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Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

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Amount of asset related to consideration paid in advance for costs that provide economic benefits in future periods, and amount of other assets that are expected to be realized or consumed within one year or the normal operating cycle, if longer.

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