Fair Value Measurement (Carrying Values And Fair Values Of The Company's Financial Instruments) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term Debt	$ 3,099,257	$ 2,819,263
Long-term Debt, Fair Value	3,166,375	2,863,355
Term-A Facility [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term Debt	737,140	1,245,175
Long-term Debt, Fair Value	748,125	1,254,855
4.75% Senior Notes Due 2025 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term Debt	784,757
Long-term Debt, Fair Value	793,000
5.00% Senior Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term Debt	984,056	981,949
Long-term Debt, Fair Value	1,012,500	1,002,500
4.75% Senior Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term Debt	593,304	592,139
Long-term Debt, Fair Value	$ 612,750	$ 606,000