Debt Schedule of Convertible Debt (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014
3.75% Convertible Senior Subordinated Notes, due 2025 [Member]
Debt Instrument [Line Items]
Debt Instrument, Convertible, Carrying Amount of Equity Component	$ 11,437
Remaining amortization period for the debt discount (in years)	11 years 274 days
Debt Instrument, Interest Rate, Effective Percentage	8.25%
4.00% Junior Subordinated Convertible Debentures, due 2033 [Member]
Debt Instrument [Line Items]
Debt Instrument, Convertible, Carrying Amount of Equity Component	118,348
Remaining amortization period for the debt discount (in years)	19 years 91 days
Debt Instrument, Interest Rate, Effective Percentage	8.01%
3.25% Convertible Senior Debentures, Due 2035 [Member]
Debt Instrument [Line Items]
Debt Instrument, Convertible, Carrying Amount of Equity Component	245,433
Remaining amortization period for the debt discount (in years)	1 year 274 days
Debt Instrument, Interest Rate, Effective Percentage	7.63%
3.75% Convertible Senior Subordinated Notes Due 2042 [Member]
Debt Instrument [Line Items]
Debt Instrument, Convertible, Carrying Amount of Equity Component	167,941
Remaining amortization period for the debt discount (in years)	28 years
Debt Instrument, Interest Rate, Effective Percentage	7.30%
3.5% Convertible senior subordinated debt [Domain]
Debt Instrument [Line Items]
Debt Instrument, Convertible, Carrying Amount of Equity Component	$ 208,200
Remaining amortization period for the debt discount (in years)	29 years 329 days
Debt Instrument, Interest Rate, Effective Percentage	7.70%