Quarterly report pursuant to Section 13 or 15(d)

Derivative Instruments and Hedging Activities Schedule of Derivative Assets and Liabilities Offset on the Balance Sheet (Details)

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Derivative Instruments and Hedging Activities Schedule of Derivative Assets and Liabilities Offset on the Balance Sheet (Details) (USD $)
In Thousands, unless otherwise specified
Mar. 31, 2013
Dec. 31, 2012
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Asset, Fair Value, Gross Asset $ 511,749 $ 462,080
Derivative Liability, Fair Value, Gross Liability 45,423 129,294
Derivative Financial Instruments, Assets [Member]
   
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Asset, Fair Value, Gross Asset 514,190 464,483
Derivative Asset, Fair Value, Gross Liability (2,441) (2,403)
Derivative Asset, Fair Value, Net 511,749 462,080
Derivative Financial Instruments, Liabilities [Member]
   
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Liability, Fair Value, Gross Liability (50,172) (129,658)
Derivative Liability, Fair Value, Gross Asset 4,749 364
Derivative Liability, Fair Value, Net $ (45,423) $ (129,294)