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

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Schedule of Derivative Instruments, Gain (Loss) in Statement of Financial Performance (Details) (USD $)
In Thousands, unless otherwise specified
3 Months Ended 9 Months Ended
Sep. 30, 2014
Sep. 30, 2013
Sep. 30, 2014
Sep. 30, 2013
Derivative Instruments, Gain (Loss) [Line Items]        
Gain (Loss) on Interest Rate Derivative Instruments Not Designated as Hedging Instruments $ 28,519 $ (55,410) $ (193,028) $ 223,388
Derivative Instruments, Gain (Loss) Recognized in Income, Net 6,056 20,434 (12,345) 66,055
Gain (Loss) on Interest Rate Swap and Swaption Agreements     (81,805) 293,783
Gain (Loss) on Mortgage Loans Held-for-Sale (2,387) (4,443) 6,233 (25,262)
Trading Activity, Gains and Losses, Net 33,129 (34,976) (203,073) 269,428
Agency To-be-Announced Securities, Non-Risk Management [Member]
       
Derivative Instruments, Gain (Loss) [Line Items]        
Derivative Instruments, Gain (Loss) Recognized in Income, Net 0 10,322 (4,701) 668
Inverse Interest-Only Securities [Member]
       
Derivative Instruments, Gain (Loss) [Line Items]        
Derivative Instruments, Gain (Loss) Recognized in Income, Net 7,567 5,686 41,942 (33,234)
Forward Purchase Commitments [Member]
       
Derivative Instruments, Gain (Loss) [Line Items]        
Gain (Loss) on Mortgage Loans Held-for-Sale (1,446) 0 2,300 (20,015)
Interest Rate Risk Associated with the Investment Portfolio [Member] | Forward Contracts [Member]
       
Derivative Instruments, Gain (Loss) [Line Items]        
Derivative Instruments, Gain (Loss) Recognized in Income, Net 1,031 71,751 (46,749) 138,429
Interest Rate Risk Associated with the Investment Portfolio [Member] | Options Held [Member]
       
Derivative Instruments, Gain (Loss) [Line Items]        
Derivative Instruments, Gain (Loss) Recognized in Income, Net (3,825) (37,052) (10,144) 15,375
Interest Rate Risk Associated with the Investment Portfolio [Member] | Swap [Member]
       
Derivative Instruments, Gain (Loss) [Line Items]        
Derivative Instruments, Gain (Loss) Recognized in Income, Net 1,306 71 6,734 (13,986)
Interest Rate Risk Associated with the Investment Portfolio [Member] | Short US Treasury Securities [Member]
       
Derivative Instruments, Gain (Loss) [Line Items]        
Derivative Instruments, Gain (Loss) Recognized in Income, Net 0 0 (8) (991)
Interest Rate Risk Associated with the Investment Portfolio [Member] | Interest Rate Swaption [Member]
       
Derivative Instruments, Gain (Loss) [Line Items]        
Gain (Loss) on Interest Rate Derivative Instruments Not Designated as Hedging Instruments (22,827) 3,711 (192,635) 95,476
Interest Rate Risk Associated with the Investment Portfolio [Member] | Total Return Swap [Member]
       
Derivative Instruments, Gain (Loss) [Line Items]        
Derivative Instruments, Gain (Loss) Recognized in Income, Net 48 0 (1,324) 0
Interest Rate Risk Associated with the Investment Portfolio [Member] | Short [Member] | Interest Rate Swap [Member]
       
Derivative Instruments, Gain (Loss) [Line Items]        
Gain (Loss) on Interest Rate Derivative Instruments Not Designated as Hedging Instruments (2,749) 7,852 104,193 7,852
Interest Rate Risk Associated with the Investment Portfolio [Member] | Long [Member] | Interest Rate Swap [Member]
       
Derivative Instruments, Gain (Loss) [Line Items]        
Gain (Loss) on Interest Rate Derivative Instruments Not Designated as Hedging Instruments 21,288 (8,691) (38,473) (8,371)
Interest Rate Risk Associated with Borrowings [Member] | Long [Member] | Interest Rate Swap [Member]
       
Derivative Instruments, Gain (Loss) [Line Items]        
Gain (Loss) on Interest Rate Derivative Instruments Not Designated as Hedging Instruments 32,807 (58,282) (66,113) 128,431
Credit Risk Associated with Non-Agency RMBS and Mortgage Loans Held-for-Sale [Member] | Credit Default Swap, Selling Protection [Member]
       
Derivative Instruments, Gain (Loss) [Line Items]        
Derivative Instruments, Gain (Loss) Recognized in Income, Net $ (71) $ (30,344) $ 1,905 $ (40,206)