Annual report pursuant to Section 13 and 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 $)
Dec. 31, 2011
Dec. 31, 2010
Derivatives, Fair Value [Line Items]    
Inverse Interest-only Securities, Accrued Interest $ 2,200,000  
Not Designated as Hedging Instrument [Member]
   
Derivatives, Fair Value [Line Items]    
Notional Amount of Derivatives 1,131,084,000 219,459,000
Derivative, Unamortized Premium 0 0
Derivative, Designated Credit Reserve 0 0
Derivative, Net, Unamortized (973,066,000) (190,162,000)
Derivative, Amortized Cost Basis 158,018,000 29,297,000
Derivative, Gross Unrealized Gains 4,606,000 1,902,000
Derivative, Gross Unrealized Losses (7,385,000) (665,000)
Derivative, Carrying Value 155,239,000 30,534,000
Derivative Financial Instruments, Assets [Member]
   
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Net 251,856,000 38,109,000
Inverse Interest-Only Securities [Member] | Derivative Financial Instruments, Assets [Member]
   
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Net $ 157,421,000 $ 30,944,000