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

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

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Carrying value as of the balance sheet date of Notes with the highest claim on the assets of the issuer in case of bankruptcy or liquidation (with maturities initially due after one year or beyond the operating cycle if longer), excluding current portion. Senior note holders are paid off in full before any payments are made to junior note holders.

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Fair Value Measurements (Details) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014	Oct. 03, 2012	Nov. 25, 2009	Jun. 01, 2007
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| Natural Gas Derivative Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value of Derivative Assets		$ 0.0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| Natural Gas Basis Derivative Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value of Derivative Assets	$ 0.0	0.0
Fair Value of Derivative Liabilities		0.0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Natural Gas Derivative Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value of Derivative Assets		2.4
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Natural Gas Basis Derivative Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value of Derivative Assets	0.1	0.1
Fair Value of Derivative Liabilities		0.1
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member] \| Natural Gas Derivative Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value of Derivative Assets		0.0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member] \| Natural Gas Basis Derivative Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value of Derivative Assets	0.0	0.0
Fair Value of Derivative Liabilities		0.0
Fair Value, Measurements, Recurring [Member] \| Estimate of Fair Value Measurement [Member] \| Natural Gas Derivative Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value of Derivative Assets		2.4
Fair Value, Measurements, Recurring [Member] \| Estimate of Fair Value Measurement [Member] \| Natural Gas Basis Derivative Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value of Derivative Assets	0.1	0.1
Fair Value of Derivative Liabilities		0.1
Senior Notes [Member] \| Senior Notes Due 2017 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of senior notes	141.9	153.0
Carrying value of senior notes	250.0	250.0
Debt Instrument, Interest Rate, Stated Percentage					7.125%
Senior Notes [Member] \| Senior Notes Due 2020 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of senior notes	96.1	133.1
Carrying value of senior notes	223.0	222.8
Debt Instrument, Interest Rate, Stated Percentage				8.875%
Senior Notes [Member] \| Senior Notes Due 2022 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of senior notes	157.2	198.0
Carrying value of senior notes	$ 404.2	$ 404.5
Debt Instrument, Interest Rate, Stated Percentage			7.875%