Debt Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Long-term Debt, Gross	$ 2,331,410	$ 2,346,488
Debt Instrument, Unamortized Discount	372,804	382,212
4.75% Senior Notes, due 2022 [Member]
Long-term Debt, Gross	400,000	400,000
Long-term Debt, Fair Value	426,000	408,000
5.00% Senior Notes, due 2024 [Member]
Long-term Debt, Gross	300,000	300,000
Long-term Debt, Fair Value	324,000	316,700
3.75% Convertible Senior Subordinated Notes, due 2025 [Member]
Long-term Debt, Gross	79,966	79,972
Long-term Debt, Fair Value	282,900	211,900
Long-term Debt	54,886	54,148
Debt Instrument, Unamortized Discount	25,080	25,824
4.00% Junior Subordinated Convertible Debentures, due 2033 [Member]
Long-term Debt, Gross	304,898	306,683
Long-term Debt, Fair Value	704,300	550,200
Long-term Debt	188,883	188,550
Debt Instrument, Unamortized Discount	116,015	118,133
3.25% Convertible Senior Debentures, Due 2035 [Member]
Long-term Debt, Gross	186,033	186,033
Long-term Debt, Fair Value	228,900	197,000
Long-term Debt	182,094	178,284
Debt Instrument, Unamortized Discount	3,939	7,749
3.25% Convertible Senior Subordinated Exchange Debentures, due 2035 [Member]
Long-term Debt, Gross	241,467	241,467
Long-term Debt	218,504	216,738
Debt Instrument, Unamortized Discount	22,963	24,729
3.50% Convertible Senior Subordianted Notes, Due 2044 [Member]
Long-term Debt, Gross	424,250	424,250
Long-term Debt, Fair Value	599,500	507,000
Long-term Debt	219,443	218,474
Debt Instrument, Unamortized Discount	$ 204,807	$ 205,776