Annual report pursuant to Section 13 and 15(d)

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

v3.19.1
Derivative Instruments and Hedging Activities Schedule of Total Return Swaps (Details) - USD ($)
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Derivative [Line Items]      
Notional $ 36,528,169,000 $ 31,226,878,000 $ 18,802,500,000
Total Return Swap [Member]      
Derivative [Line Items]      
Notional 48,265,000 63,507,000  
Fair Value (383,000) (106,000)  
Cost Basis (59,000) 567,000  
Derivative, Unrealized Gains (Losses) (324,000) (673,000)  
Total Return Swap [Member] | Maturity Date, 1/12/2043 [Member]      
Derivative [Line Items]      
Notional 21,395,000 24,362,000  
Fair Value (153,000) (24,000)  
Cost Basis (30,000) 201,000  
Derivative, Unrealized Gains (Losses) (123,000) (225,000)  
Total Return Swap [Member] | Maturity Date, 1/12/2044 [Member]      
Derivative [Line Items]      
Notional 26,870,000 39,145,000  
Fair Value (230,000) (82,000)  
Cost Basis (29,000) 366,000  
Derivative, Unrealized Gains (Losses) $ (201,000) $ (448,000)