Quarterly report pursuant to Section 13 or 15(d)

Derivative Instruments and Hedging Activities Schedule of Total Return Swaps (Details)

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Derivative Instruments and Hedging Activities Schedule of Total Return Swaps (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)
Total Return Swap [Member]
            
Derivative [Line Items]            
Derivative, Notional Amount (576,478)   (49,629)      
Derivative, Fair Value, Net (678)   (134)      
Derivative, Cost (1,583)   (453)      
Derivative, Unrealized Gains (Losses) (2,261)   (587)      
Maturity Date, 1/12/2043 [Member] | Total Return Swap [Member]
            
Derivative [Line Items]            
Derivative, Notional Amount (432,105)   (49,629)      
Derivative, Fair Value, Net (464)   (134)      
Derivative, Cost (1,457)   (453)      
Derivative, Unrealized Gains (Losses) (1,921)   (587)      
Maturity Date, 1/12/2044 [Member] | Total Return Swap [Member]
            
Derivative [Line Items]            
Derivative, Notional Amount (144,373)          
Derivative, Fair Value, Net (214)          
Derivative, Cost (126)          
Derivative, Unrealized Gains (Losses) $ (340)