Debt (Schedule of Carrying Values of Debt) (Interest Rates) (Details)	Dec. 31, 2014	Dec. 31, 2013
Capital Lease Obligations [Member]
Debt Instrument [Line Items]
Debt instrument, weighted average interest rate (percentage)	2.80%
Notes Payable [Member] | Equipment [Member]
Debt Instrument [Line Items]
Debt instrument, weighted average interest rate (percentage)	2.80%
4.875% Senior Notes [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate (percentage)	4.875%
2011 4.0% Notes [Member] | Convertible Debt [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate (percentage)		4.00%
2011 4.25% Notes [Member] | Convertible Debt [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate (percentage)		4.25%
2009 4.0% Notes [Member] | Convertible Debt [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate (percentage)		4.00%
2009 4.25% Notes [Member] | Convertible Debt [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate (percentage)		4.25%