Quarterly report pursuant to Section 13 or 15(d)

Derivative Instruments and Hedging Activities Schedule of Inverse Interest-Only Securities Reconciliation (Details)

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Derivative Instruments and Hedging Activities Schedule of Inverse Interest-Only Securities Reconciliation (Details) (USD $)
Mar. 31, 2012
Dec. 31, 2011
Derivatives, Fair Value [Line Items]    
Inverse Interest-only Securities, Accrued Interest $ 3,100,000  
Not Designated as Hedging Instrument [Member]
   
Derivatives, Fair Value [Line Items]    
Notional Amount of Derivatives 1,666,707,000 1,131,084,000
Derivative, Unamortized Premium 0 0
Derivative, Designated Credit Reserve 0 0
Derivative, Net, Unamortized (1,424,110,000) (973,066,000)
Derivative, Amortized Cost Basis 242,597,000 158,018,000
Derivative, Gross Unrealized Gains 9,475,000 4,606,000
Derivative, Gross Unrealized Losses (9,127,000) (7,385,000)
Derivative, Carrying Value 242,945,000 155,239,000
Derivative Financial Instruments, Assets [Member]
   
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Net 340,715,000 251,856,000
Inverse Interest-Only Securities [Member] | Derivative Financial Instruments, Assets [Member]
   
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Net $ 246,066,000 $ 157,421,000