Quarterly report pursuant to Section 13 or 15(d)

Derivative Instruments and Hedging Activities Put and Call Options for TBAs (Details)

v3.8.0.1
Derivative Instruments and Hedging Activities Put and Call Options for TBAs (Details) - USD ($)
Sep. 30, 2017
Jun. 30, 2017
Dec. 31, 2016
Sep. 30, 2016
Jun. 30, 2016
Dec. 31, 2015
Derivative [Line Items]            
Notional $ 24,113,321,000 $ 16,988,116,000 $ 18,802,500,000 $ 22,062,904,000 $ 26,141,370,000 $ 21,998,381,000
Derivative Financial Instruments, Liabilities [Member]            
Derivative [Line Items]            
Notional 6,800,429,000   3,543,593,000      
Fair Value (11,312,000)   (12,501,000)      
Derivative Financial Instruments, Assets [Member]            
Derivative [Line Items]            
Notional 20,122,892,000   21,708,907,000      
Fair Value 238,305,000   324,182,000      
Options Held [Member] | Derivative Financial Instruments, Liabilities [Member]            
Derivative [Line Items]            
Notional 0   0      
Fair Value 0   0      
Options Held [Member] | Derivative Financial Instruments, Assets [Member]            
Derivative [Line Items]            
Notional 2,000,000,000   1,136,000,000      
Fair Value 156,000   42,633,000      
Options Held [Member] | Long [Member]            
Derivative [Line Items]            
Notional $ 2,000,000,000   2,500,000,000      
Options Held [Member] | Short [Member]            
Derivative [Line Items]            
Notional     $ 3,636,000,000