v3.2.0.727
FAIR VALUE OF FINANCIAL INSTRUMENTS (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2014
Jun. 30, 2015
4.625 Notes    
Carrying amount and estimated fair values of debt    
Interest rate (as a percent) 4.625% 4.625%
4.875 Notes    
Carrying amount and estimated fair values of debt    
Interest rate (as a percent) 4.875% 4.875%
Term Loan Due 2017    
Carrying amount and estimated fair values of debt    
Debt issuance costs $ 1.8  
Term Loan Due 2022    
Carrying amount and estimated fair values of debt    
Interest rate (as a percent)   4.00%
Debt issuance costs and discounts   $ 2.8
Carrying Amount | Level 1 | 4.625 Notes    
Carrying amount and estimated fair values of debt    
Long-term debt 688.0 688.0
Carrying Amount | Level 1 | 4.875 Notes    
Carrying amount and estimated fair values of debt    
Long-term debt 450.0 450.0
Carrying Amount | Level 2 | Commodity contracts    
Carrying amount and estimated fair values of debt    
Commodity purchase contracts (12.9) (3.4)
Carrying Amount | Level 2 | Term Loan Due 2017    
Carrying amount and estimated fair values of debt    
Long-term debt 192.6  
Carrying Amount | Level 2 | Term Loan Due 2022    
Carrying amount and estimated fair values of debt    
Long-term debt   246.0
Fair Value | Level 1 | 4.625 Notes    
Carrying amount and estimated fair values of debt    
Long-term debt 651.9 675.1
Fair Value | Level 1 | 4.875 Notes    
Carrying amount and estimated fair values of debt    
Long-term debt 426.7 436.8
Fair Value | Level 2 | Commodity contracts    
Carrying amount and estimated fair values of debt    
Commodity purchase contracts (12.9) (3.4)
Fair Value | Level 2 | Term Loan Due 2017    
Carrying amount and estimated fair values of debt    
Long-term debt $ 194.4  
Fair Value | Level 2 | Term Loan Due 2022    
Carrying amount and estimated fair values of debt    
Long-term debt   $ 250.9