Other Financial Statement Disclosures (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Fair value [Member]
Fair values of Financial Instruments [Abstract]
5% Senior Notes, due 2017	$ 431,076	$ 445,568
7.875% Senior Notes, due 2019	600,063	617,076
4.875% Senior Notes, due 2022	719,252	761,509
5.4% Senior Notes, due 2042	358,411	406,493
Total	2,108,802	2,230,646
Carrying value [Member]
Fair values of Financial Instruments [Abstract]
5% Senior Notes, due 2017	398,818	398,678
7.875% Senior Notes, due 2019	498,005	497,842
4.875% Senior Notes, due 2022	713,998	714,775
5.4% Senior Notes, due 2042	398,331	398,303
Total	$ 2,009,152	$ 2,009,598