Fair Value Measurements (Details 1) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Fair Value of Financial Instruments
Carrying Value	$ 4,848,529	$ 4,693,004
Fair Value	5,413,397	5,187,676
5.375% Senior Notes Due August 2012 [Member]
Fair Value of Financial Instruments
Carrying Value	274,761	274,604
Fair Value	279,824	281,188
6.15% Senior Notes Due February 2018 [Member]
Fair Value of Financial Instruments
Carrying Value	967,794	967,490
Fair Value	1,119,300	1,113,986
9.25% Senior Notes Due January 2019 [Member]
Fair Value of Financial Instruments
Carrying Value	1,125,000	1,125,000
Fair Value	1,451,734	1,419,514
5.00% senior notes due September 2020 [Member]
Fair Value of Financial Instruments
Carrying Value	697,419	697,343
Fair Value	751,275	734,475
4.625% senior notes due September 2021 [Member]
Fair Value of Financial Instruments
Carrying Value	697,727	697,667
Fair Value	733,124	708,176
Subsidiary preferred stock [Member]
Fair Value of Financial Instruments
Carrying Value	69,188	69,188
Fair Value	67,500	68,625
Revolving Credit Facilities [Member]
Fair Value of Financial Instruments
Carrying Value	1,010,000	860,000
Fair Value	1,010,000	860,000
Other [Member]
Fair Value of Financial Instruments
Carrying Value	640	1,712
Fair Value	$ 640	$ 1,712