Fair Value Measurements (Details) (USD $)	Mar. 31, 2015		Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt, aggregate fair value	$ 2,175,000,000		$ 2,166,000,000
Long-term debt, aggregate carrying amount, net of unamortized discounts	2,104,112,000		2,146,599,000
Recurring Basis [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	135,000	[1]	187,000	[1]
Recurring Basis [Member] | Interest Rate Swap [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest rate swaps	11,509,000		10,254,000
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Recurring Basis [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	135,000	[1]	187,000	[1]
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Recurring Basis [Member] | Interest Rate Swap [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest rate swaps	0		0
Significant Other Observable Inputs (Level 2) [Member] | Recurring Basis [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	[1]	0	[1]
Significant Other Observable Inputs (Level 2) [Member] | Recurring Basis [Member] | Interest Rate Swap [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest rate swaps	11,509,000		10,254,000
Significant Unobservable Inputs (Level 3) [Member] | Recurring Basis [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	[1]	0	[1]
Significant Unobservable Inputs (Level 3) [Member] | Recurring Basis [Member] | Interest Rate Swap [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest rate swaps	$ 0		$ 0

[1] (a) Available-for-sale securities are included in Other assets, net in the accompanying Condensed Consolidated Balance Sheets.