Quarterly report pursuant to Section 13 or 15(d)

Derivative Instruments and Hedging Activities Schedule of Credit Default Swaps, Receive Protection (Details)

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Derivative Instruments and Hedging Activities Schedule of Credit Default Swaps, Receive Protection (Details) (Credit Default Swap, Buying Protection [Member], USD $)
In Thousands, unless otherwise specified
 3 Months Ended
Mar. 31, 2013
Mar. 31, 2012
Dec. 31, 2012
Derivative [Line Items]      
Derivative, Average Implied Credit Spread 253.96   254.06
Derivative, Notional Amount $ (437,496)   $ (438,440)
Derivative, Fair Value, Net 47,238   52,906
Derivative, Cost (81,788)   (81,788)
Gain (Loss) on Credit Risk Derivatives, Net (34,550)   (28,882)
Maturity Date, 09/20/2013 [Member]
      
Derivative [Line Items]      
Derivative, Maturity Date Sep. 20, 2013 Sep. 20, 2013  
Derivative, Average Implied Credit Spread 460.00   460.00
Derivative, Notional Amount (45,000)   (45,000)
Derivative, Fair Value, Net (183)   (264)
Derivative, Cost (3,127)   (3,127)
Gain (Loss) on Credit Risk Derivatives, Net (3,310)   (3,391)
Maturity Date, 12/20/2013 [Member]
      
Derivative [Line Items]      
Derivative, Maturity Date Dec. 20, 2013 Dec. 20, 2013  
Derivative, Average Implied Credit Spread 181.91   181.91
Derivative, Notional Amount (105,000)   (105,000)
Derivative, Fair Value, Net (167)   (198)
Derivative, Cost (3,225)   (3,225)
Gain (Loss) on Credit Risk Derivatives, Net (3,392)   (3,423)
Maturity Date, 06/20/2016 [Member]
      
Derivative [Line Items]      
Derivative, Maturity Date Jun. 20, 2016 Jun. 20, 2016  
Derivative, Average Implied Credit Spread 105.50   105.50
Derivative, Notional Amount (100,000)   (100,000)
Derivative, Fair Value, Net (2,091)   (1,940)
Derivative, Cost (260)   (260)
Gain (Loss) on Credit Risk Derivatives, Net (2,351)   (2,200)
Maturity Date, 12/20/2016 [Member]
      
Derivative [Line Items]      
Derivative, Maturity Date Dec. 20, 2016 Dec. 20, 2016  
Derivative, Average Implied Credit Spread 496.00   496.00
Derivative, Notional Amount (25,000)   (25,000)
Derivative, Fair Value, Net 41   527
Derivative, Cost (4,062)   (4,062)
Gain (Loss) on Credit Risk Derivatives, Net (4,021)   (3,535)
Maturity Date, 05/25/2046 [Member]
      
Derivative [Line Items]      
Derivative, Maturity Date May 25, 2046 May 25, 2046  
Derivative, Average Implied Credit Spread 297.60   297.60
Derivative, Notional Amount (162,496)   (163,440)
Derivative, Fair Value, Net 49,638   54,781
Derivative, Cost (71,114)   (71,114)
Gain (Loss) on Credit Risk Derivatives, Net $ (21,476)   $ (16,333)