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Derivative Instruments and Hedging Activities Schedule of Derivative Instruments, Gain (Loss) in Statement of Financial Performance (Details)

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Derivative Instruments and Hedging Activities Schedule of Derivative Instruments, Gain (Loss) in Statement of Financial Performance (Details) (USD $)
In Thousands, unless otherwise specified
 3 Months Ended
Mar. 31, 2013
Mar. 31, 2012
Derivative Instruments, Gain (Loss) [Line Items]    
Derivative Instruments, Gain (Loss) Recognized in Income, Net $ 2,597 $ (25,083)
Gain (loss) on Interest Rate Swap and Swaption Agreements 18,972 (16,193)
Gain (Loss) on Mortgage Loans Held-for-Sale 14,323 (32)
Other Contract [Member]
    
Derivative Instruments, Gain (Loss) [Line Items]    
Derivative Instruments, Gain (Loss) Recognized in Income, Net (12,249) (2,637)
Interest Rate Swaps and Swaptions Associated with U.S. Treasuries and TBA Contracts [Member]
    
Derivative Instruments, Gain (Loss) [Line Items]    
Gain (loss) on Interest Rate Swap and Swaption Agreements (89) (1,648)
Forward Purchase Commitment [Member]
    
Derivative Instruments, Gain (Loss) [Line Items]    
Gain (Loss) on Mortgage Loans Held-for-Sale 287 13
Interest Rate Swaps and Swaptions Associated with Repurchase Agreements [Member]
    
Derivative Instruments, Gain (Loss) [Line Items]    
Gain (loss) on Interest Rate Swap and Swaption Agreements 19,061 (14,545)
Credit Default Swap, Selling Protection [Member]
    
Derivative Instruments, Gain (Loss) [Line Items]    
Derivative Instruments, Gain (Loss) Recognized in Income, Net (5,643) (24,301)
Credit Default Swap, Buying Protection [Member]
    
Derivative Instruments, Gain (Loss) [Line Items]    
Derivative Instruments, Gain (Loss) Recognized in Income, Net 0 8,220
Inverse Interest-Only Securities [Member]
    
Derivative Instruments, Gain (Loss) [Line Items]    
Derivative Instruments, Gain (Loss) Recognized in Income, Net $ 1,230 $ 9,815