Debt Fair Value of Financial Instruments (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Long-term Debt, Gross	$ 2,493,127	$ 2,500,434
Debt Instrument, Unamortized Discount	566,927	573,082
7.75% Senior Subordinated Notes, Due 2020 [Member]
Long-term Debt, Gross	400,000	400,000
Long-term Debt, Fair Value	430,300	435,800
3.75% Convertible Senior Subordinated Notes, due 2025 [Member]
Long-term Debt, Gross	132,375	132,408
Long-term Debt, Fair Value	299,200	306,500
Long-term Debt	87,848	87,310
Debt Instrument, Unamortized Discount	44,527	45,098
4.00% Junior Subordinated Convertible Debentures, due 2033 [Member]
Long-term Debt, Gross	307,122	307,153
Long-term Debt, Fair Value	450,300	455,900
Long-term Debt	186,773	186,136
Debt Instrument, Unamortized Discount	120,349	121,017
3.25% Convertible Senior Debentures, Due 2035 [Member]
Long-term Debt, Gross	427,500	427,500
Long-term Debt, Fair Value	454,800	457,400
Long-term Debt	397,146	393,126
Debt Instrument, Unamortized Discount	30,354	34,374
3.75% Convertible Senior Subordinated Notes Due 2042 [Member]
Long-term Debt, Gross	390,000	390,000
Long-term Debt, Fair Value	582,600	592,800
Long-term Debt	225,465	225,014
Debt Instrument, Unamortized Discount	164,535	164,986
3.50% Convertible Senior Subordianted Notes, Due 2044 [Member]
Long-term Debt, Gross	424,250	424,250
Long-term Debt, Fair Value	432,600	428,500
Long-term Debt	217,088	216,643
Debt Instrument, Unamortized Discount	$ 207,162	$ 207,607