Debt (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Long-term debt
Other	$ 490	$ 437
Long-term Debt	4,380,193	4,379,700
Current portion of long-term debt	435	364
Long-term debt	4,379,758	4,379,336
6.15% senior notes due February 2018
Long-term debt
Senior Notes	969,012	968,708
Interest rate on senior note due (as a percent)	6.15%
9.25% senior notes due January 2019
Long-term debt
Senior Notes	1,125,000	1,125,000
Interest rate on senior note due (as a percent)	9.25%
5.00% senior notes due September 2020
Long-term debt
Senior Notes	697,724	697,648
Interest rate on senior note due (as a percent)	5.00%
4.625% senior notes due September 2021
Long-term debt
Senior Notes	697,967	697,907
Interest rate on senior note due (as a percent)	4.625%
Revolving Credit Facility
Long-term debt
Revolving credit facility	$ 890,000	$ 890,000