v3.5.0.2
Fair Value of Financial Instruments - Summary of Carrying Amounts and Estimated Fair Values of Long-Term Debt and Commodity Purchase Contracts (Detail) - USD ($)
$ in Millions
6 Months Ended 12 Months Ended
Jun. 30, 2016
Jun. 30, 2015
Dec. 31, 2015
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Debt issuance costs   $ 3.5  
4.625 Notes [Member]      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Interest rate (as a percent) 4.625%   4.625%
Debt issuance costs $ 8.8   $ 9.6
4.875 Notes [Member]      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Interest rate (as a percent) 4.875%   4.875%
Debt issuance costs $ 5.4   $ 5.8
Term Loan Due 2022 [Member]      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Deferred financing fees 2.8   3.1
Level 1 [Member] | Carrying Reported Amount Fair Value Disclosure [Member] | 4.625 Notes [Member]      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Long-term debt 679.2   678.4
Level 1 [Member] | Carrying Reported Amount Fair Value Disclosure [Member] | 4.875 Notes [Member]      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Long-term debt 444.6   444.2
Level 1 [Member] | Estimate of Fair Value Fair Value Disclosure [Member] | 4.625 Notes [Member]      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Long-term debt 703.5   635.1
Level 1 [Member] | Estimate of Fair Value Fair Value Disclosure [Member] | 4.875 Notes [Member]      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Long-term debt 461.3   408.4
Level 2 [Member] | Carrying Reported Amount Fair Value Disclosure [Member] | Term Loan Due 2022 [Member]      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Long-term debt 243.5   244.4
Level 2 [Member] | Carrying Reported Amount Fair Value Disclosure [Member] | Commodity Contracts [Member]      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Commodity purchase contracts 1.2   (0.4)
Level 2 [Member] | Estimate of Fair Value Fair Value Disclosure [Member] | Term Loan Due 2022 [Member]      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Long-term debt 246.6   247.8
Level 2 [Member] | Estimate of Fair Value Fair Value Disclosure [Member] | Commodity Contracts [Member]      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Commodity purchase contracts $ 1.2   $ (0.4)