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 ($)
$ in Thousands
Mar. 31, 2016
Dec. 31, 2015
Mar. 31, 2015
Dec. 31, 2014
Derivatives, Fair Value [Line Items]        
Interest Receivable $ 54,517 $ 49,970    
Derivative, Notional Amount 26,390,596 21,998,381 $ 33,709,043 $ 48,115,523
Derivative Financial Instruments, Assets [Member]        
Derivatives, Fair Value [Line Items]        
Derivative, Fair Value, Net 197,847 271,509    
Derivative, Notional Amount 17,869,498 21,735,997    
Inverse Interest-Only Securities [Member]        
Derivatives, Fair Value [Line Items]        
Derivative, Fair Value, Net 158,786 159,582    
Interest Receivable 1,567 1,676    
Derivative, Notional Amount 882,726 932,037 $ 1,106,210 $ 1,168,226
Derivative, Unamortized Premium 0 0    
Derivative, Designated Credit Reserve 0 0    
Derivative, Net, Unamortized (750,622) (792,178)    
Derivative, Amortized Cost Basis 132,104 139,859    
Derivative, Gross Unrealized Gains 25,538 19,655    
Derivative, Gross Unrealized Losses (423) (1,608)    
Derivative, Carrying Value 157,219 157,906    
Inverse Interest-Only Securities [Member] | Derivative Financial Instruments, Assets [Member]        
Derivatives, Fair Value [Line Items]        
Derivative, Notional Amount $ 882,726 $ 932,037