Fair Value Measurements (Details 2) (USD $)	Jun. 30, 2011	Dec. 31, 2010
7.5% Senior Subordinated Notes due 2013 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior Subordinated Notes, Carrying Amount	$ 0	$ 224,563,000
Senior Subordinated Notes, Estimated Fair Value	0	228,375,000
7.5% Senior Subordinated Notes due 2015 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior Subordinated Notes, Carrying Amount	0	300,427,000
Senior Subordinated Notes, Estimated Fair Value	0	310,500,000
9.5% Senior Subordinated Notes due 2016 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior Subordinated Notes, Carrying Amount	238,142,000	239,509,000
Senior Subordinated Notes, Estimated Fair Value	249,942,000	249,661,000
9.75% Senior Subordinated Notes due 2016 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior Subordinated Notes, Carrying Amount	406,354,000	404,211,000
Senior Subordinated Notes, Estimated Fair Value	476,446,000	475,380,000
8.25% Senior Subordinated Notes due 2020 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior Subordinated Notes, Carrying Amount	996,273,000	996,273,000
Senior Subordinated Notes, Estimated Fair Value	1,085,938,000	1,080,956,000
6 3/8% Senior Subordinated Notes Due 2021 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior Subordinated Notes, Carrying Amount	400,000,000	0
Senior Subordinated Notes, Estimated Fair Value	$ 400,000,000	$ 0