Fair Value Measurements and Derivative Instruments (Details) (Fair Value, Measurements, Nonrecurring, USD $) In Thousands, unless otherwise specified	Mar. 31, 2015		Dec. 31, 2014
Level 1
Assets:
Cash and cash equivalents	$ 229,705	[1],[2]	$ 189,241	[1],[2]
Total Assets	229,705	[2]	189,241	[2]
Liabilities:
Long-term debt (including current portion of long-term debt)	1,868,909	[2],[3]	1,859,361	[2],[3]
Total Liabilities	1,868,909	[2]	1,859,361	[2]
Level 2
Assets:
Cash and cash equivalents	0	[1]	0	[1]
Total Assets	0		0
Liabilities:
Long-term debt (including current portion of long-term debt)	6,995,000	[3]	6,902,053	[3]
Total Liabilities	6,995,000		6,902,053
Level 3
Assets:
Cash and cash equivalents	0	[1]	0	[1]
Total Assets	0		0
Liabilities:
Long-term debt (including current portion of long-term debt)	0	[3]	0	[3]
Total Liabilities	0		0
Total Carrying Amount
Assets:
Cash and cash equivalents	229,705	[1]	189,241	[1]
Total Assets	229,705		189,241
Liabilities:
Long-term debt (including current portion of long-term debt)	8,502,921	[3]	8,391,301	[3]
Total Liabilities	8,502,921		8,391,301
Total Fair Value
Assets:
Cash and cash equivalents	229,705	[1]	189,241	[1]
Total Assets	229,705		189,241
Liabilities:
Long-term debt (including current portion of long-term debt)	8,863,909	[3]	8,761,414	[3]
Total Liabilities	$ 8,863,909		$ 8,761,414

[1] Consists of cash and marketable securities with original maturities of less than 90 days.

[2] Inputs based on quoted prices (unadjusted) in active markets for identical assets or liabilities that we have the ability to access. Valuation of these items does not entail a significant amount of judgment.

[3] Consists of unsecured revolving credit facilities, senior notes, senior debentures and term loans. Does not include our capital lease obligations.