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)

v3.5.0.2
Derivative Instruments and Hedging Activities Schedule of Interest Rate Swap Receivers Associated with the Investment Portfolio (Details)
$ in Thousands
Jun. 30, 2016
USD ($)
Mar. 31, 2016
USD ($)
Dec. 31, 2015
USD ($)
Jun. 30, 2015
USD ($)
Mar. 31, 2015
USD ($)
Dec. 31, 2014
USD ($)
Derivative [Line Items]            
Derivative, Notional Amount $ 26,141,370 $ 26,390,596 $ 21,998,381 $ 27,401,335 $ 33,709,043 $ 48,115,523
Interest Rate Swap [Member]            
Derivative [Line Items]            
Derivative, Notional Amount 13,697,000 $ 15,425,513 14,268,806 $ 16,225,523 $ 19,929,000 $ 18,584,000
Interest Rate Risk Associated with the Investment Portfolio [Member] | Interest Rate Swap [Member] | Short [Member]            
Derivative [Line Items]            
Derivative, Notional Amount $ 3,064,000   $ 3,164,000      
Derivative, Average Variable Interest Rate 1.784%   2.145%      
Derivative, Average Fixed Interest Rate 0.645%   0.431%      
Derivative, Average Remaining Period Until Maturity 4.80   6.26      
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] | Short [Member]            
Derivative [Line Items]            
Derivative, Notional Amount $ 575,000   $ 575,000      
Derivative, Average Variable Interest Rate 1.44%   1.44%      
Derivative, Average Fixed Interest Rate 0.654%   0.329%      
Derivative, Average Remaining Period Until Maturity 2.39   2.89      
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 $ 500,000          
Derivative, Average Variable Interest Rate 1.042%          
Derivative, Average Fixed Interest Rate 0.635%          
Derivative, Average Remaining Period Until Maturity 2.56          
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 $ 1,989,000   $ 2,589,000      
Derivative, Average Variable Interest Rate 2.07%   2.301%      
Derivative, Average Fixed Interest Rate 0.646%   0.453%      
Derivative, Average Remaining Period Until Maturity 6.06   7.00