Quarterly report pursuant to Section 13 or 15(d)

Derivative Instruments and Hedging Activities Schedule of Average Notional Amounts of Derivative Positions (Details)

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Derivative Instruments and Hedging Activities Schedule of Average Notional Amounts of Derivative Positions (Details) (USD $)
In Thousands, unless otherwise specified
 3 Months Ended
Mar. 31, 2012
Mar. 31, 2011
Inverse Interest-Only Securities [Member]
    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Notional Amount $ 1,330,835  
Derivative Liability, Notional Amount 0  
Interest Rate Swap [Member]
    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Notional Amount 0  
Derivative Liability, Notional Amount 6,366,593 1,300,000
Credit Default Swap [Member]
    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Notional Amount 541,888  
Derivative Liability, Notional Amount 137,567  
Interest Rate Swaption [Member]
    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Notional Amount 3,573,077  
Derivative Liability, Notional Amount 0  
Other Contract [Member]
    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Notional Amount 207,418  
Derivative Liability, Notional Amount 754,396  
Forward Sale Commitment [Member]
    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Notional Amount 5,186  
Derivative Liability, Notional Amount $ 0