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 ($)
Mar. 31, 2018
Dec. 31, 2017
Mar. 31, 2017
Dec. 31, 2016
Derivative [Line Items]        
Notional $ 18,429,288,000 $ 31,226,878,000 $ 15,935,535,000 $ 18,802,500,000
Derivative Financial Instruments, Assets [Member]        
Derivative [Line Items]        
Notional 25,956,767,000 25,503,371,000    
Fair Value 274,048,000 309,918,000    
Derivative Financial Instruments, Liabilities [Member]        
Derivative [Line Items]        
Notional 12,752,521,000 8,335,507,000    
Fair Value (46,074,000) (31,903,000)    
Options Held [Member] | Derivative Financial Instruments, Assets [Member]        
Derivative [Line Items]        
Notional 785,000,000      
Fair Value 872,000 0    
Options Held [Member] | Derivative Financial Instruments, Liabilities [Member]        
Derivative [Line Items]        
Notional 845,000,000      
Fair Value (6,957,000) 0    
Options Held [Member] | Long [Member]        
Derivative [Line Items]        
Notional 7,573,000,000 0    
Options Held [Member] | Short [Member]        
Derivative [Line Items]        
Notional $ 7,600,000,000 $ 0