Fair Value Measurements (Details 2) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Fair Value of Financial Instruments
Carrying Value	$ 4,748,473	$ 4,693,004
Fair Value	5,379,838	5,187,676
Carrying Value	69,188	69,188
Fair Value	68,625	68,625
5.375% Senior Notes Due August 2012
Fair Value of Financial Instruments
Carrying Value		274,604
Fair Value		281,188
Interest rate on senior note due (as a percent)	5.375%
6.15% Senior Notes Due February 2018
Fair Value of Financial Instruments
Carrying Value	968,403	967,490
Fair Value	1,155,180	1,113,986
Interest rate on senior note due (as a percent)	6.15%
9.25% Senior Notes Due January 2019
Fair Value of Financial Instruments
Carrying Value	1,125,000	1,125,000
Fair Value	1,470,139	1,419,514
Interest rate on senior note due (as a percent)	9.25%
5.00% senior notes due September 2020
Fair Value of Financial Instruments
Carrying Value	697,572	697,343
Fair Value	769,146	734,475
Interest rate on senior note due (as a percent)	5.00%
4.625% senior notes due September 2021
Fair Value of Financial Instruments
Carrying Value	697,847	697,667
Fair Value	726,285	708,176
Interest rate on senior note due (as a percent)	4.625%
Revolving Credit Facility
Fair Value of Financial Instruments
Carrying Value	1,190,000	860,000
Fair Value	1,190,000	860,000
Other
Fair Value of Financial Instruments
Carrying Value	463	1,712
Fair Value	$ 463	$ 1,712