Fair Value Measurements and Derivative Instruments (Details) (Fair Value, Measurements, Nonrecurring, USD $) In Thousands, unless otherwise specified	Mar. 31, 2014		Dec. 31, 2013
Total
Assets:
Cash and cash equivalents	$ 216,508	[1]	$ 204,687	[1]
Total Assets	216,508		204,687
Liabilities:
Long-term debt (including current portion of long-term debt)	8,319,299	[2]	8,431,220	[2]
Total Liabilities	8,319,299		8,431,220
Level 1
Assets:
Cash and cash equivalents	216,508	[1],[3]	204,687	[1],[3]
Total Assets	216,508	[3]	204,687	[3]
Liabilities:
Long-term debt (including current portion of long-term debt)	1,893,376	[2],[3]	2,888,255	[2],[3]
Total Liabilities	1,893,376	[3]	2,888,255	[3]
Level 2
Assets:
Cash and cash equivalents	0	[1],[4]	0	[1],[4]
Total Assets	0	[4]	0	[4]
Liabilities:
Long-term debt (including current portion of long-term debt)	6,425,923	[2],[4]	5,542,965	[2],[4]
Total Liabilities	6,425,923	[4]	5,542,965
Level 3
Assets:
Cash and cash equivalents	0	[1],[5]	0	[1],[5]
Total Assets	0	[5]	0	[5]
Liabilities:
Long-term debt (including current portion of long-term debt)	0	[2],[5]	0	[2],[5]
Total Liabilities	0	[5]	0	[5]
Reported Value Measurement
Assets:
Cash and cash equivalents	216,508	[1]	204,687	[1]
Total Assets	216,508		204,687
Liabilities:
Long-term debt (including current portion of long-term debt)	7,942,449	[2]	8,020,061	[2]
Total Liabilities	$ 7,942,449		$ 8,020,061

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

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

[3] 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.

[4] Inputs other than quoted prices included within Level 1 that are observable for the liability, either directly or indirectly. For unsecured revolving credit facilities and unsecured term loans, fair value is determined utilizing the income valuation approach. This valuation model takes into account the contract terms of our debt such as the debt maturity and the interest rate on the debt.

[5] Inputs that are unobservable. The Company did not use any Level 3 inputs as of March 31, 2014 and December 31, 2013.