Annual report pursuant to Section 13 and 15(d)

Financial Instruments - Notional Amounts of Derivative Instruments (Details)

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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