Indebtedness (Details) (USD $) In Thousands	Jun. 30, 2011	Dec. 31, 2010
Indebtedness
Bank debt	$ 0	$ 274,000
Subordinated debt:
Subordinated debt	1,787,398	1,686,536
Total debt	1,787,398	1,960,536
6.375% Senior Subordinated Notes due 2015 [Member]
Subordinated debt:
Subordinated debt	0	150,000
7.5% senior subordinated notes due 2016, net of discount [Member]
Subordinated debt:
Subordinated debt	0	249,683
7.5% Senior Subordinated Notes due 2017 [Member]
Subordinated debt:
Subordinated debt	250,000	250,000
7.25% Senior Subordinated Notes due 2018 [Member]
Subordinated debt:
Subordinated debt	250,000	250,000
8.0% senior subordinated notes due 2019, net of discount [Member]
Subordinated debt:
Subordinated debt	287,398	286,853
6.75% Senior Subordinated Notes due 2020 [Member]
Subordinated debt:
Subordinated debt	500,000	500,000
5.75% Senior Subordinated Notes due 2021 [Member]
Subordinated debt:
Subordinated debt	$ 500,000	$ 0