Debt Schedule of Convertible Debt (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2013
3.75% Convertible Senior Subordinated Notes, due 2025 [Member]
Debt Instrument [Line Items]
Debt Instrument, Convertible, Carrying Amount of Equity Component	$ 27,230
Remaining amortization period for the debt discount (in years)	12 years 183 days
Effective interest rates for the liability components of Convertible Debentures (in hundredths)	8.25%
4.00% Junior Subordinated Convertible Debentures, due 2033 [Member]
Debt Instrument [Line Items]
Debt Instrument, Convertible, Carrying Amount of Equity Component	151,665
Remaining amortization period for the debt discount (in years)	20 years
Effective interest rates for the liability components of Convertible Debentures (in hundredths)	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)	2 years 183 days
Effective interest rates for the liability components of Convertible Debentures (in hundredths)	7.63%
3.75% Convertible Senior Subordinated Notes Due 2042 [Member]
Debt Instrument [Line Items]
Debt Instrument, Convertible, Carrying Amount of Equity Component	$ 161,600
Remaining amortization period for the debt discount (in years)	28 years 274 days
Effective interest rates for the liability components of Convertible Debentures (in hundredths)	7.11%