Quarterly report pursuant to Section 13 or 15(d)

FAIR VALUE, Fair Value of Other Financial Instruments (Details)

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FAIR VALUE, Fair Value of Other Financial Instruments (Details)
$ in Millions
Sep. 30, 2015
USD ($)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Long-term Debt $ 867.7
Debt instrument, unamortized discount 2.3
Asset retirement obligations 0.4
Carrying Amount [Member]  
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Senior unsecured notes 697.5
Revolving credit facility 170.0
Estimated Fair Value [Member]  
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Senior unsecured notes $ 526.5