Quarterly report pursuant to Section 13 or 15(d)

Schedule of Derivative Instruments in Statement of Financial Position, Fair Value (Details)

v3.8.0.1
Schedule of Derivative Instruments in Statement of Financial Position, Fair Value (Details) - USD ($)
Mar. 31, 2018
Dec. 31, 2017
Mar. 31, 2017
Dec. 31, 2016
Notional Disclosures [Abstract]        
Notional $ 18,429,288,000 $ 31,226,878,000 $ 15,935,535,000 $ 18,802,500,000
Inverse Interest-Only Securities [Member]        
Derivative, Fair Value, Net [Abstract]        
Fair Value 82,388,000 91,827,000    
Notional Disclosures [Abstract]        
Notional 558,942,274 588,245,610    
Total Return Swap [Member]        
Derivative, Fair Value, Net [Abstract]        
Fair Value (176,000) (106,000)    
Notional Disclosures [Abstract]        
Notional 61,521,000 63,507,000    
Derivative Financial Instruments, Assets [Member]        
Derivative, Fair Value, Net [Abstract]        
Fair Value 274,048,000 309,918,000    
Notional Disclosures [Abstract]        
Notional 25,956,767,000 25,503,371,000    
Derivative Financial Instruments, Assets [Member] | Inverse Interest-Only Securities [Member]        
Notional Disclosures [Abstract]        
Notional 558,942,274 588,245,610    
Derivative Financial Instruments, Assets [Member] | Interest Rate Swap [Member]        
Derivative, Fair Value, Net [Abstract]        
Fair Value 175,525,000 206,773,000    
Notional Disclosures [Abstract]        
Notional 18,932,825,000 21,516,125,000    
Derivative Financial Instruments, Assets [Member] | Interest Rate Swaption [Member]        
Derivative, Fair Value, Net [Abstract]        
Fair Value 7,146,000 10,405,000    
Notional Disclosures [Abstract]        
Notional 2,115,000,000 2,666,000,000    
Derivative Financial Instruments, Assets [Member] | Forward Contracts [Member]        
Derivative, Fair Value, Net [Abstract]        
Fair Value 8,117,000 913,000    
Notional Disclosures [Abstract]        
Notional 3,565,000,000 733,000,000    
Derivative Financial Instruments, Assets [Member] | Options Held [Member]        
Derivative, Fair Value, Net [Abstract]        
Fair Value 872,000 0    
Notional Disclosures [Abstract]        
Notional 785,000,000      
Derivative Financial Instruments, Assets [Member] | Total Return Swap [Member]        
Derivative, Fair Value, Net [Abstract]        
Fair Value 0 0    
Notional Disclosures [Abstract]        
Notional 0 0    
Derivative Financial Instruments, Liabilities [Member]        
Derivative, Fair Value, Net [Abstract]        
Fair Value (46,074,000) (31,903,000)    
Notional Disclosures [Abstract]        
Notional 12,752,521,000 8,335,507,000    
Derivative Financial Instruments, Liabilities [Member] | Inverse Interest-Only Securities [Member]        
Derivative, Fair Value, Net [Abstract]        
Fair Value 0 0    
Notional Disclosures [Abstract]        
Notional 0 0    
Derivative Financial Instruments, Liabilities [Member] | Interest Rate Swap [Member]        
Derivative, Fair Value, Net [Abstract]        
Fair Value 0 (29,867,000)    
Notional Disclosures [Abstract]        
Notional 4,666,000,000 6,966,000,000    
Derivative Financial Instruments, Liabilities [Member] | Interest Rate Swaption [Member]        
Derivative, Fair Value, Net [Abstract]        
Fair Value (18,977,000) 0    
Notional Disclosures [Abstract]        
Notional 4,060,000,000 0    
Derivative Financial Instruments, Liabilities [Member] | Forward Contracts [Member]        
Derivative, Fair Value, Net [Abstract]        
Fair Value (19,964,000) (1,930,000)    
Notional Disclosures [Abstract]        
Notional 3,120,000,000 1,306,000,000    
Derivative Financial Instruments, Liabilities [Member] | Options Held [Member]        
Derivative, Fair Value, Net [Abstract]        
Fair Value (6,957,000) 0    
Notional Disclosures [Abstract]        
Notional 845,000,000      
Derivative Financial Instruments, Liabilities [Member] | Total Return Swap [Member]        
Derivative, Fair Value, Net [Abstract]        
Fair Value (176,000) (106,000)    
Notional Disclosures [Abstract]        
Notional $ 61,521,204 $ 63,507,327