Quarterly report pursuant to Section 13 or 15(d)

Derivative Instruments and Hedging Activities Schedule of Interest Rate Swap Receivers Associated with the Investment Portfolio (Details)

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Derivative Instruments and Hedging Activities Schedule of Interest Rate Swap Receivers Associated with the Investment Portfolio (Details) (USD $)
In Thousands, unless otherwise specified
Sep. 30, 2014
Jun. 30, 2014
Dec. 31, 2013
Sep. 30, 2013
Jun. 30, 2013
Dec. 31, 2012
Derivative [Line Items]            
Derivative, Notional Amount $ 57,015,981 $ 43,379,217 $ 37,366,610 $ 36,472,401 $ 44,262,605 $ 22,377,656
Interest Rate Swap [Member]
           
Derivative [Line Items]            
Derivative, Notional Amount 27,770,655 23,628,148 19,619,000 17,575,000 18,485,000 14,070,000
Interest Rate Risk Associated with the Investment Portfolio [Member] | Interest Rate Swap [Member] | Short [Member]
           
Derivative [Line Items]            
Derivative, Notional Amount 3,276,477   2,154,000      
Derivative, Average Variable Interest Rate 2.521%   2.337%      
Derivative, Average Fixed Interest Rate 0.235%   0.24%      
Derivative, Average Remaining Period Until Maturity 8.62   7.84      
Interest Rate Risk Associated with the Investment Portfolio [Member] | Derivative Maturity Over Three And Within Four Years From Balance Sheet Date [Member] | Interest Rate Swap [Member] | Short [Member]
           
Derivative [Line Items]            
Derivative, Notional Amount 575,000          
Derivative, Average Variable Interest Rate 1.44%          
Derivative, Average Fixed Interest Rate 0.234%          
Derivative, Average Remaining Period Until Maturity 4.14          
Interest Rate Risk Associated with the Investment Portfolio [Member] | Derivative Maturity Over Four Years From Balance Sheet Date [Member] | Interest Rate Swap [Member] | Short [Member]
           
Derivative [Line Items]            
Derivative, Notional Amount $ 2,701,477   $ 2,154,000      
Derivative, Average Variable Interest Rate 2.751%   2.337%      
Derivative, Average Fixed Interest Rate 0.235%   0.24%      
Derivative, Average Remaining Period Until Maturity 9.57   7.84