Fair Value of Assets and Liabilities (Details 2) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 Senior Notes, due 2012 at 6.85%	Apr. 11, 2012 Senior Notes, due 2012 at 6.85%	Dec. 31, 2011 Senior Notes, due 2012 at 6.85%	Dec. 31, 2012 Senior Notes, due 2013 at 6.75%	Sep. 10, 2012 Senior Notes, due 2013 at 6.75%	Dec. 31, 2011 Senior Notes, due 2013 at 6.75%	Dec. 31, 2012 Senior Notes, due 2014 at 7.875%	Dec. 31, 2011 Senior Notes, due 2014 at 7.875%	Dec. 31, 2012 Senior Notes, due 2015 at 5.125%	Dec. 31, 2011 Senior Notes, due 2015 at 5.125%	Dec. 31, 2012 Senior Notes, due 2016 at 6.3%	Dec. 31, 2011 Senior Notes, due 2016 at 6.3%	Dec. 31, 2012 Senior Notes, due 2017 at 5.625%	Dec. 31, 2011 Senior Notes, due 2017 at 5.625%	Dec. 31, 2012 Senior Notes, due 2018 at 6.7%	Dec. 31, 2011 Senior Notes, due 2018 at 6.7%	Dec. 31, 2012 Senior Notes, due 2022 at 5%	Aug. 16, 2012 Senior Notes, due 2022 at 5%	Dec. 31, 2012 Convertible senior notes, due 2027 at 3.8%	Mar. 20, 2012 Convertible senior notes, due 2027 at 3.8%	Dec. 31, 2011 Convertible senior notes, due 2027 at 3.8%	Dec. 31, 2012 Carrying Amount	Dec. 31, 2011 Carrying Amount	Dec. 31, 2011 Carrying Amount Senior Notes, due 2012 at 6.85%	Dec. 31, 2011 Carrying Amount Senior Notes, due 2013 at 6.75%	Dec. 31, 2012 Carrying Amount Senior Notes, due 2014 at 7.875%	Dec. 31, 2011 Carrying Amount Senior Notes, due 2014 at 7.875%	Dec. 31, 2012 Carrying Amount Senior Notes, due 2015 at 5.125%	Dec. 31, 2011 Carrying Amount Senior Notes, due 2015 at 5.125%	Dec. 31, 2012 Carrying Amount Senior Notes, due 2016 at 6.3%	Dec. 31, 2011 Carrying Amount Senior Notes, due 2016 at 6.3%	Dec. 31, 2012 Carrying Amount Senior Notes, due 2017 at 5.625%	Dec. 31, 2011 Carrying Amount Senior Notes, due 2017 at 5.625%	Dec. 31, 2012 Carrying Amount Senior Notes, due 2018 at 6.7%	Dec. 31, 2011 Carrying Amount Senior Notes, due 2018 at 6.7%	Dec. 31, 2012 Carrying Amount Senior Notes, due 2022 at 5%	Dec. 31, 2012 Carrying Amount Convertible senior notes, due 2027 at 3.8%	Dec. 31, 2011 Carrying Amount Convertible senior notes, due 2027 at 3.8%	Dec. 31, 2012 Fair Value	Dec. 31, 2011 Fair Value	Dec. 31, 2011 Fair Value Senior Notes, due 2012 at 6.85%	Dec. 31, 2011 Fair Value Senior Notes, due 2013 at 6.75%	Dec. 31, 2012 Fair Value Senior Notes, due 2014 at 7.875%	Dec. 31, 2011 Fair Value Senior Notes, due 2014 at 7.875%	Dec. 31, 2012 Fair Value Senior Notes, due 2015 at 5.125%	Dec. 31, 2011 Fair Value Senior Notes, due 2015 at 5.125%	Dec. 31, 2012 Fair Value Senior Notes, due 2016 at 6.3%	Dec. 31, 2011 Fair Value Senior Notes, due 2016 at 6.3%	Dec. 31, 2012 Fair Value Senior Notes, due 2017 at 5.625%	Dec. 31, 2011 Fair Value Senior Notes, due 2017 at 5.625%	Dec. 31, 2012 Fair Value Senior Notes, due 2018 at 6.7%	Dec. 31, 2011 Fair Value Senior Notes, due 2018 at 6.7%	Dec. 31, 2012 Fair Value Senior Notes, due 2022 at 5%	Dec. 31, 2012 Fair Value Convertible senior notes, due 2027 at 3.8%	Dec. 31, 2011 Fair Value Convertible senior notes, due 2027 at 3.8%
Fair Value of Assets and Liabilities
Financial liabilities	$ 2,733,478				$ 100,829			$ 287,000	$ 300,000	$ 300,000	$ 280,000	$ 280,000	$ 275,000	$ 275,000	$ 300,000	$ 300,000	$ 350,000	$ 350,000	$ 500,000		$ 8,478		$ 79,054			$ 100,829	$ 287,000	$ 300,000	$ 300,000	$ 280,000	$ 280,000	$ 275,000	$ 275,000	$ 300,000	$ 300,000	$ 350,000	$ 350,000	$ 500,000	$ 8,478	$ 79,054			$ 105,407	$ 301,871	$ 333,360	$ 333,887	$ 298,926	$ 290,052	$ 306,078	$ 291,572	$ 335,173	$ 313,106	$ 417,293	$ 386,942	$ 531,343	$ 9,092	$ 80,087
Unamortized discounts	(11,120)	(5,169)																			0		231	(11,120)	(5,169)
Financial liabilities																								$ 2,002,358	$ 1,966,714																$ 2,231,265	$ 2,102,924
Interest rate stated percentage			6.85%	6.85%	6.85%	6.75%	6.75%	6.75%	7.875%	7.875%	5.125%	5.125%	6.30%	6.30%	5.625%	5.625%	6.70%	6.70%	5.00%	5.00%	3.80%	3.80%	3.80%