Income Taxes (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Income taxes
Valuation allowance	$ 0	$ 0
Unrecognized tax benefits	7.9us-gaap_UnrecognizedTaxBenefits	7.9us-gaap_UnrecognizedTaxBenefits
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	1.6	1.6
State
Income taxes
Net operating loss resulting from repairs and maintenance deductions	49.9	49.9
Federal
Income taxes
Net operating loss resulting from repairs and maintenance deductions	$ 43.8	$ 43.8

Amount of deferred tax assets for which it is more likely than not that a tax benefit will not be realized.

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Amount of operating loss carryforward, before tax effects, available to reduce future taxable income under enacted tax laws.

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Amount of unrecognized tax benefits pertaining to uncertain tax positions taken in tax returns.

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The total amount of unrecognized tax benefits that, if recognized, would affect the effective tax rate.

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