Financial Instruments - Notional Amounts of Derivative Instruments (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012
Derivative [Line Items]
Percentage of Debt Hedged by Interest Rate Derivatives	75.00%
Variable Rate Loan converted to Fixed Rate	$ 20.0
Notional Amount of Interest Rate Derivatives	2,900.0
Interest Rate Contract [Member] | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative, Average Fixed Interest Rate	1.98%
Notional Amount of Interest Rate Derivatives	0
Interest Rate Contract [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative, Average Fixed Interest Rate	1.98%
Notional Amount of Interest Rate Derivatives	0
Maximum [Member] | Interest Rate Contract [Member] | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Notional Amount of Interest Rate Derivatives	0
Maximum [Member] | Interest Rate Contract [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Notional Amount of Interest Rate Derivatives	$ 0