Fair Value of Assets and Liabilities (Details 2) (USD $) In Thousands, unless otherwise specified																1 Months Ended
	Jun. 30, 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%	Jun. 30, 2012 Senior Notes, due 2013 at 6.75%	Dec. 31, 2011 Senior Notes, due 2013 at 6.75%	Jun. 30, 2012 Senior Notes, due 2014 at 7.875%	Dec. 31, 2011 Senior Notes, due 2014 at 7.875%	Jun. 30, 2012 Senior Notes, due 2015 at 5.125%	Dec. 31, 2011 Senior Notes, due 2015 at 5.125%	Jun. 30, 2012 Senior Notes, due 2016 at 6.3%	Dec. 31, 2011 Senior Notes, due 2016 at 6.3%	Jun. 30, 2012 Senior Notes, due 2017 at 5.625%	Dec. 31, 2011 Senior Notes, due 2017 at 5.625%	Jun. 30, 2012 Senior Notes, due 2018 at 6.7%	Dec. 31, 2011 Senior Notes, due 2018 at 6.7%	Mar. 31, 2012 Convertible senior notes, due 2027 at 3.8%	Jun. 30, 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%	Jun. 30, 2011 Convertible senior notes, due 2027 at 3.8%	Jun. 30, 2012 Carrying Amount	Dec. 31, 2011 Carrying Amount	Dec. 31, 2011 Carrying Amount Senior Notes, due 2012 at 6.85%	Jun. 30, 2012 Carrying Amount Senior Notes, due 2013 at 6.75%	Dec. 31, 2011 Carrying Amount Senior Notes, due 2013 at 6.75%	Jun. 30, 2012 Carrying Amount Senior Notes, due 2014 at 7.875%	Dec. 31, 2011 Carrying Amount Senior Notes, due 2014 at 7.875%	Jun. 30, 2012 Carrying Amount Senior Notes, due 2015 at 5.125%	Dec. 31, 2011 Carrying Amount Senior Notes, due 2015 at 5.125%	Jun. 30, 2012 Carrying Amount Senior Notes, due 2016 at 6.3%	Dec. 31, 2011 Carrying Amount Senior Notes, due 2016 at 6.3%	Jun. 30, 2012 Carrying Amount Senior Notes, due 2017 at 5.625%	Dec. 31, 2011 Carrying Amount Senior Notes, due 2017 at 5.625%	Jun. 30, 2012 Carrying Amount Senior Notes, due 2018 at 6.7%	Dec. 31, 2011 Carrying Amount Senior Notes, due 2018 at 6.7%	Jun. 30, 2012 Carrying Amount Convertible senior notes, due 2027 at 3.8%	Dec. 31, 2011 Carrying Amount Convertible senior notes, due 2027 at 3.8%	Jun. 30, 2012 Fair Value	Dec. 31, 2011 Fair Value	Dec. 31, 2011 Fair Value Senior Notes, due 2012 at 6.85%	Jun. 30, 2012 Fair Value Senior Notes, due 2013 at 6.75%	Dec. 31, 2011 Fair Value Senior Notes, due 2013 at 6.75%	Jun. 30, 2012 Fair Value Senior Notes, due 2014 at 7.875%	Dec. 31, 2011 Fair Value Senior Notes, due 2014 at 7.875%	Jun. 30, 2012 Fair Value Senior Notes, due 2015 at 5.125%	Dec. 31, 2011 Fair Value Senior Notes, due 2015 at 5.125%	Jun. 30, 2012 Fair Value Senior Notes, due 2016 at 6.3%	Dec. 31, 2011 Fair Value Senior Notes, due 2016 at 6.3%	Jun. 30, 2012 Fair Value Senior Notes, due 2017 at 5.625%	Dec. 31, 2011 Fair Value Senior Notes, due 2017 at 5.625%	Jun. 30, 2012 Fair Value Senior Notes, due 2018 at 6.7%	Dec. 31, 2011 Fair Value Senior Notes, due 2018 at 6.7%	Jun. 30, 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																					$ 1,796,312	$ 1,966,714	$ 100,829	$ 287,000	$ 287,000	$ 300,000	$ 300,000	$ 280,000	$ 280,000	$ 275,000	$ 275,000	$ 300,000	$ 300,000	$ 350,000	$ 350,000	$ 8,478	$ 79,054
Unamortized discounts																			231		(4,166)	(5,169)
Financial liabilities																																						1,946,507	2,102,924	105,407	299,175	301,871	331,964	333,887	292,464	290,052	295,881	291,572	320,655	313,106	397,576	386,942	8,792	80,087
Interest rate stated percentage	6.85%	6.85%	6.85%	6.75%	6.75%	7.875%	7.875%	5.125%	5.125%	6.30%	6.30%	5.625%	5.625%	6.70%	6.70%		3.80%	3.80%	3.80%	3.80%
Repurchase of convertible senior notes																$ 70,576