Fair Value Measurements Estimated Fair Values and Carrying Amounts (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt	$ 2,922,600	$ 2,919,185
Senior Secured Credit Agreement | Term B Loans
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt	188,038	187,725
Senior Secured Credit Agreement | Term B Loans | Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long term debt	189,150	189,704
Senior Secured Credit Agreement | Term C Loans
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt	1,645,828	1,644,109
Senior Secured Credit Agreement | Term C Loans | Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long term debt	1,661,728	1,666,942
5.875% Senior Notes due 2022 | Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt	1,088,734	1,087,351
5.875% Senior Notes due 2022 | Senior Notes | Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long term debt	$ 1,109,229	$ 1,132,417