Debt Fair Value of Financial Instruments (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Long-term Debt, Gross	$ 2,433,533	$ 2,500,434
Debt Instrument, Unamortized Discount	543,264	573,082
7.75% Senior Subordinated Notes, Due 2020 [Member]
Long-term Debt, Gross	400,000	400,000
Long-term Debt, Fair Value	434,200	435,800
3.75% Convertible Senior Subordinated Notes, due 2025 [Member]
Long-term Debt, Gross	80,009	132,408
Long-term Debt, Fair Value	196,600	306,500
Long-term Debt	53,468	87,310
Debt Instrument, Unamortized Discount	26,541	45,098
4.00% Junior Subordinated Convertible Debentures, due 2033 [Member]
Long-term Debt, Gross	307,122	307,153
Long-term Debt, Fair Value	501,000	455,900
Long-term Debt	187,441	186,136
Debt Instrument, Unamortized Discount	119,681	121,017
3.25% Convertible Senior Debentures, Due 2035 [Member]
Long-term Debt, Gross	427,500	427,500
Long-term Debt, Fair Value	455,900	457,400
Long-term Debt	401,243	393,126
Debt Instrument, Unamortized Discount	26,257	34,374
3.75% Convertible Senior Subordinated Notes Due 2042 [Member]
Long-term Debt, Gross	390,000	390,000
Long-term Debt, Fair Value	643,500	592,800
Long-term Debt	225,923	225,014
Debt Instrument, Unamortized Discount	164,077	164,986
3.50% Convertible Senior Subordianted Notes, Due 2044 [Member]
Long-term Debt, Gross	424,250	424,250
Long-term Debt, Fair Value	492,100	428,500
Long-term Debt	217,542	216,643
Debt Instrument, Unamortized Discount	$ 206,708	$ 207,607