Quarterly report pursuant to Section 13 or 15(d)

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

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Derivative Instruments and Hedging Activities Schedule of Interest Rate Swap Payers Associated with the Investment Portfolio (Details) (USD $)
In Thousands, unless otherwise specified
Jun. 30, 2014
Mar. 31, 2014
Dec. 31, 2013
Jun. 30, 2013
Mar. 31, 2013
Dec. 31, 2012
Derivative [Line Items]            
Derivative, Notional Amount $ 43,379,217 $ 43,576,146 $ 37,366,610 $ 44,262,605 $ 27,041,328 $ 22,377,656
Interest Rate Swap [Member]
           
Derivative [Line Items]            
Derivative, Notional Amount 23,628,148 21,663,148 19,619,000 18,485,000 16,685,000 14,070,000
Interest Rate Risk Associated with the Investment Portfolio [Member] | Interest Rate Swap [Member] | Long [Member]
           
Derivative [Line Items]            
Derivative, Notional Amount 3,940,000   3,040,000      
Derivative, Average Fixed Interest Rate 1.595%   1.363%      
Derivative, Average Variable Interest Rate 0.23%   0.24%      
Derivative, Average Remaining Period Until Maturity 4.39   4.20      
Interest Rate Risk Associated with the Investment Portfolio [Member] | Derivative Maturity Within One Year From Balance Sheet Date [Member] | Interest Rate Swap [Member] | Long [Member]
           
Derivative [Line Items]            
Derivative, Notional Amount              
Derivative, Average Fixed Interest Rate              
Derivative, Average Variable Interest Rate              
Derivative, Average Remaining Period Until Maturity 0.00   0.00      
Interest Rate Risk Associated with the Investment Portfolio [Member] | Derivative Maturity Over One And Within Two Years From Balance Sheet Date [Member] | Interest Rate Swap [Member] | Long [Member]
           
Derivative [Line Items]            
Derivative, Notional Amount 1,000,000           
Derivative, Average Fixed Interest Rate 0.955%           
Derivative, Average Variable Interest Rate 0.228%           
Derivative, Average Remaining Period Until Maturity 2.17   0.00      
Interest Rate Risk Associated with the Investment Portfolio [Member] | Derivative Maturity Over Two And Within Three Years From Balance Sheet Date [Member] | Interest Rate Swap [Member] | Long [Member]
           
Derivative [Line Items]            
Derivative, Notional Amount      1,000,000      
Derivative, Average Fixed Interest Rate      0.955%      
Derivative, Average Variable Interest Rate      0.239%      
Derivative, Average Remaining Period Until Maturity 0.00   2.67      
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] | Long [Member]
           
Derivative [Line Items]            
Derivative, Notional Amount 2,040,000           
Derivative, Average Fixed Interest Rate 1.563%           
Derivative, Average Variable Interest Rate 0.23%           
Derivative, Average Remaining Period Until Maturity 4.44   0.00      
Interest Rate Risk Associated with the Investment Portfolio [Member] | Derivative Maturity Over Four Years From Balance Sheet Date [Member] | Interest Rate Swap [Member] | Long [Member]
           
Derivative [Line Items]            
Derivative, Notional Amount $ 900,000   $ 2,040,000      
Derivative, Average Fixed Interest Rate 2.378%   1.563%      
Derivative, Average Variable Interest Rate 0.234%   0.241%      
Derivative, Average Remaining Period Until Maturity 6.74   4.94