Fair Value of Assets and Liabilities (Details 2) (USD $) In Thousands, unless otherwise specified	Feb. 15, 2014 Senior Notes, due 2014 at 7.875%	Dec. 31, 2013 Senior Notes, due 2014 at 7.875%	Mar. 31, 2014 Senior Notes, due 2015 at 5.125%	Dec. 31, 2013 Senior Notes, due 2015 at 5.125%	Mar. 31, 2014 Senior Notes, due 2016 at 6.3%	Dec. 31, 2013 Senior Notes, due 2016 at 6.3%	Mar. 31, 2014 Senior Notes, due 2017 at 5.625%	Dec. 31, 2013 Senior Notes, due 2017 at 5.625%	Mar. 31, 2014 Senior Notes, due 2018 at 6.7%	Dec. 31, 2013 Senior Notes, due 2018 at 6.7%	Mar. 31, 2014 Senior Notes, due 2022 at 5%	Dec. 31, 2013 Senior Notes, due 2022 at 5%	Mar. 31, 2014 Senior Notes, due 2023 at 4.5%	Dec. 31, 2013 Senior Notes, due 2023 at 4.5%	Mar. 31, 2014 Senior Notes, due 2024 at 4.65%	Mar. 12, 2014 Senior Notes, due 2024 at 4.65%	Mar. 31, 2014 Convertible senior notes, due 2027 at 3.8%	Dec. 31, 2013 Convertible senior notes, due 2027 at 3.8%	Mar. 31, 2014 Carrying Amount	Dec. 31, 2013 Carrying Amount	Dec. 31, 2013 Carrying Amount Senior Notes, due 2014 at 7.875%	Mar. 31, 2014 Carrying Amount Senior Notes, due 2015 at 5.125%	Dec. 31, 2013 Carrying Amount Senior Notes, due 2015 at 5.125%	Mar. 31, 2014 Carrying Amount Senior Notes, due 2016 at 6.3%	Dec. 31, 2013 Carrying Amount Senior Notes, due 2016 at 6.3%	Mar. 31, 2014 Carrying Amount Senior Notes, due 2017 at 5.625%	Dec. 31, 2013 Carrying Amount Senior Notes, due 2017 at 5.625%	Mar. 31, 2014 Carrying Amount Senior Notes, due 2018 at 6.7%	Dec. 31, 2013 Carrying Amount Senior Notes, due 2018 at 6.7%	Mar. 31, 2014 Carrying Amount Senior Notes, due 2022 at 5%	Dec. 31, 2013 Carrying Amount Senior Notes, due 2022 at 5%	Mar. 31, 2014 Carrying Amount Senior Notes, due 2023 at 4.5%	Dec. 31, 2013 Carrying Amount Senior Notes, due 2023 at 4.5%	Mar. 31, 2014 Carrying Amount Senior Notes, due 2024 at 4.65%	Mar. 31, 2014 Carrying Amount Convertible senior notes, due 2027 at 3.8%	Dec. 31, 2013 Carrying Amount Convertible senior notes, due 2027 at 3.8%	Mar. 31, 2014 Fair Value	Dec. 31, 2013 Fair Value	Dec. 31, 2013 Fair Value Senior Notes, due 2014 at 7.875%	Mar. 31, 2014 Fair Value Senior Notes, due 2015 at 5.125%	Dec. 31, 2013 Fair Value Senior Notes, due 2015 at 5.125%	Mar. 31, 2014 Fair Value Senior Notes, due 2016 at 6.3%	Dec. 31, 2013 Fair Value Senior Notes, due 2016 at 6.3%	Mar. 31, 2014 Fair Value Senior Notes, due 2017 at 5.625%	Dec. 31, 2013 Fair Value Senior Notes, due 2017 at 5.625%	Mar. 31, 2014 Fair Value Senior Notes, due 2018 at 6.7%	Dec. 31, 2013 Fair Value Senior Notes, due 2018 at 6.7%	Mar. 31, 2014 Fair Value Senior Notes, due 2022 at 5%	Dec. 31, 2013 Fair Value Senior Notes, due 2022 at 5%	Mar. 31, 2014 Fair Value Senior Notes, due 2023 at 4.5%	Dec. 31, 2013 Fair Value Senior Notes, due 2023 at 4.5%	Mar. 31, 2014 Fair Value Senior Notes, due 2024 at 4.65%	Mar. 31, 2014 Fair Value Convertible senior notes, due 2027 at 3.8%	Dec. 31, 2013 Fair Value Convertible senior notes, due 2027 at 3.8%
Fair Value of Assets and Liabilities
Financial liabilities																					$ 300,000	$ 280,000	$ 280,000	$ 275,000	$ 275,000	$ 300,000	$ 300,000	$ 350,000	$ 350,000	$ 500,000	$ 500,000	$ 300,000	$ 300,000	$ 350,000	$ 8,478	$ 8,478			$ 304,035	$ 283,965	$ 283,150	$ 296,049	$ 297,443	$ 331,071	$ 327,681	$ 397,968	$ 399,560	$ 521,475	$ 524,810	$ 298,932	$ 289,950	$ 356,101	$ 8,860	$ 8,983
Unamortized discounts																			(9,849)	(11,120)
Financial liabilities																			$ 2,353,629	$ 2,302,358																	$ 2,494,421	$ 2,435,612
Interest rate stated percentage	7.875%	7.875%	5.125%	5.125%	6.30%	6.30%	5.625%	5.625%	6.70%	6.70%	5.00%	5.00%	4.50%	4.50%	4.65%	4.65%	3.80%	3.80%