Quarterly report pursuant to Section 13 or 15(d)

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

v3.10.0.1
Derivative Instruments and Hedging Activities Put and Call Options for TBAs (Details) - USD ($)
Sep. 30, 2018
Jun. 30, 2018
Dec. 31, 2017
Sep. 30, 2017
Jun. 30, 2017
Dec. 31, 2016
Derivative [Line Items]            
Notional $ 41,330,283,000 $ 28,618,861,000 $ 31,226,878,000 $ 24,113,321,000 $ 16,988,116,000 $ 18,802,500,000
Derivative Financial Instruments, Assets [Member]            
Derivative [Line Items]            
Notional 33,229,283,000   25,503,371,000      
Fair Value 403,231,000   309,918,000      
Derivative Financial Instruments, Liabilities [Member]            
Derivative [Line Items]            
Notional 11,521,000,000   8,335,507,000      
Fair Value (797,504,000)   (31,903,000)      
Options Held [Member] | Derivative Financial Instruments, Assets [Member]            
Derivative [Line Items]            
Notional 780,000,000          
Fair Value 4,954,000   0      
Options Held [Member] | Derivative Financial Instruments, Liabilities [Member]            
Derivative [Line Items]            
Notional 130,000,000          
Fair Value (1,329,000)   0      
Options Held [Member] | Long [Member]            
Derivative [Line Items]            
Notional 3,700,000,000   0      
Options Held [Member] | Short [Member]            
Derivative [Line Items]            
Notional $ 4,600,000,000   $ 0