Quarterly report pursuant to Section 13 or 15(d)

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

v3.7.0.1
Derivative Instruments and Hedging Activities Schedule of Total Return Swaps (Details) - USD ($)
Jun. 30, 2017
Mar. 31, 2017
Dec. 31, 2016
Jun. 30, 2016
Mar. 31, 2016
Dec. 31, 2015
Derivative [Line Items]            
Notional $ 16,988,116,000 $ 15,935,535,000 $ 18,802,500,000 $ 26,141,370,000 $ 26,390,596,000 $ 21,998,381,000
Total Return Swap [Member]            
Derivative [Line Items]            
Notional 68,629,000   90,593,000      
Fair Value 300,000   (17,000)      
Cost Basis 567,000   686,000      
Derivative, Unrealized Gains (Losses) (267,000)   (703,000)      
Total Return Swap [Member] | Maturity Date, 1/12/2043 [Member]            
Derivative [Line Items]            
Notional 26,309,245   45,083,136      
Fair Value 95,000   (5,000)      
Cost Basis 201,000   320,000      
Derivative, Unrealized Gains (Losses) (106,000)   (325,000)      
Total Return Swap [Member] | Maturity Date, 1/12/2044 [Member]            
Derivative [Line Items]            
Notional 42,319,975   45,509,532      
Fair Value 205,000   (12,000)      
Cost Basis 366,000   366,000      
Derivative, Unrealized Gains (Losses) $ (161,000)   $ (378,000)