Fair Value Measurements and Derivative Instruments (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012	Dec. 31, 2011
Assets:
Cash and cash equivalents	$ 209,567	$ 194,855	$ 241,237	$ 262,186
Fair Value, Measurements, Nonrecurring | Total
Assets:
Cash and cash equivalents	209,567	194,855
Total Assets	209,567	194,855
Liabilities:
Long-term debt (including current portion of long-term debt)	8,225,926	8,859,310
Total Liabilities	8,225,926	8,859,310
Fair Value, Measurements, Nonrecurring | Level 1
Assets:
Cash and cash equivalents	209,567	194,855
Total Assets	209,567	194,855
Liabilities:
Long-term debt (including current portion of long-term debt)	3,212,399	3,917,398
Total Liabilities	3,212,399	3,917,398
Fair Value, Measurements, Nonrecurring | Level 2
Liabilities:
Long-term debt (including current portion of long-term debt)	5,013,527	4,941,912
Total Liabilities	$ 5,013,527	$ 4,941,912