Quarterly report pursuant to Section 13 or 15(d)

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

v3.5.0.2
Derivative Instruments and Hedging Activities Schedule of Total Return Swaps (Details) - USD ($)
$ in Thousands
Jun. 30, 2016
Mar. 31, 2016
Dec. 31, 2015
Jun. 30, 2015
Mar. 31, 2015
Dec. 31, 2014
Derivative [Line Items]            
Derivative, Notional Amount $ (26,141,370) $ (26,390,596) $ (21,998,381) $ (27,401,335) $ (33,709,043) $ (48,115,523)
Total Return Swap [Member]            
Derivative [Line Items]            
Derivative, Notional Amount (588,037) $ (868,145) (889,418) $ (988,409) $ (877,529) $ (598,459)
Derivative, Fair Value, Net (7,419)   1,645      
Derivative, Cost 3,539   1,383      
Derivative, Unrealized Gains (Losses) (10,958)   262      
Maturity Date, 1/12/2043 [Member] | Total Return Swap [Member]            
Derivative [Line Items]            
Derivative, Notional Amount (275,900)   (369,639)      
Derivative, Fair Value, Net (3,455)   456      
Derivative, Cost 1,818   866      
Derivative, Unrealized Gains (Losses) (5,273)   (410)      
Maturity Date, 1/12/2044 [Member] | Total Return Swap [Member]            
Derivative [Line Items]            
Derivative, Notional Amount (257,720)   (325,003)      
Derivative, Fair Value, Net (3,187)   350      
Derivative, Cost 2,346   1,679      
Derivative, Unrealized Gains (Losses) (5,533)   (1,329)      
Maturity Date, 1/12/2045 [Member] | Total Return Swap [Member]            
Derivative [Line Items]            
Derivative, Notional Amount (54,417)   (194,776)      
Derivative, Fair Value, Net (777)   839      
Derivative, Cost (625)   1,162      
Derivative, Unrealized Gains (Losses) (152)   2,001      
Derivative Financial Instruments, Assets [Member]            
Derivative [Line Items]            
Derivative, Notional Amount (16,940,106)   (21,735,997)      
Derivative, Fair Value, Net 223,985   271,509      
Derivative Financial Instruments, Assets [Member] | Total Return Swap [Member]            
Derivative [Line Items]            
Derivative, Notional Amount 0   (889,418)      
Derivative, Fair Value, Net $ 0   $ 1,645