Annual report pursuant to Section 13 and 15(d)

Fair Value Measurements and Derivative Instruments (Carrying amounts and fair value of the financial instruments) (Details)

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Fair Value Measurements and Derivative Instruments (Carrying amounts and fair value of the financial instruments) (Details) - USD ($)
$ in Thousands
Dec. 31, 2015
Apr. 01, 2015
Dec. 31, 2014
Carrying Amount      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Current and long-term debt $ 1,348,106   $ 1,036,678
Fair Value      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Current and long-term debt $ 1,390,743   $ 1,055,952
Senior Notes [Member] | 2021 Notes      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Stated percentage 6.75% 6.75%  
Senior Notes [Member] | 2025 Notes      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Stated percentage 6.875% 6.875%