Quarterly report pursuant to Section 13 or 15(d)

DEBT OBLIGATIONS - Narrative (Details)

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DEBT OBLIGATIONS - Narrative (Details)
1 Months Ended 9 Months Ended
Aug. 15, 2016
USD ($)
Jul. 15, 2016
USD ($)
May 09, 2016
USD ($)
Mar. 31, 2016
USD ($)
Jun. 30, 2016
USD ($)
Apr. 30, 2016
USD ($)
Sep. 30, 2016
USD ($)
Sep. 30, 2015
USD ($)
May 31, 2016
USD ($)
Debt Instrument [Line Items]                  
Face amount of debt             $ 12,782,716,000    
Repayments of Debt             $ 6,786,408,000 $ 5,445,381,000  
Percent decline in equity, first period             50.00%    
Decline in equity, first period (in months)             12 months    
Percent decline in equity, second period             35.00%    
Decline in equity, second period (in months)             3 months    
Ratio of indebtedness to tangible net worth             4    
Unamortized Deferred Financing Costs [Member]                  
Debt Instrument [Line Items]                  
Loss on extinguishment of debt       $ 100,000          
Two Year Servicer Advance Facility [Member]                  
Debt Instrument [Line Items]                  
Maximum borrowing capacity     $ 185,000,000            
Debt instrument, term (in years)     2 years            
Advance Financing Facility [Member]                  
Debt Instrument [Line Items]                  
Maximum borrowing capacity                 $ 950,000,000
NRART 2015-T1 [Member]                  
Debt Instrument [Line Items]                  
Loss on extinguishment of debt   $ 200,000              
Repayments of Debt   $ 400,000,000              
NRART 2015-T3 [Member]                  
Debt Instrument [Line Items]                  
Loss on extinguishment of debt $ 700,000                
Repayments of Debt $ 400,000,000                
Repurchase Agreements [Member] | Total Repurchase Agreements [Member]                  
Debt Instrument [Line Items]                  
Face amount of debt [1]             $ 4,931,731,000    
Secured Debt [Member] | 4.75% Senior Notes Maturing April 2018 [Member]                  
Debt Instrument [Line Items]                  
Face amount of debt           $ 225,000,000.0      
Secured Debt [Member] | 4.75% Senior Notes Maturing June 2019 [Member]                  
Debt Instrument [Line Items]                  
Face amount of debt         $ 101,200,000.0        
Maximum borrowing capacity         300,000,000.0        
Secured Debt [Member] | Term Loans Maturing June 2019 [Member]                  
Debt Instrument [Line Items]                  
Face amount of debt         400,000,000        
Face amount, amount voluntarily retained         $ 20,900,000.0        
London Interbank Offered Rate (LIBOR) [Member] | Secured Debt [Member] | 4.75% Senior Notes Maturing April 2018 [Member]                  
Debt Instrument [Line Items]                  
Variable interest rate spread           4.75%      
London Interbank Offered Rate (LIBOR) [Member] | Secured Debt [Member] | 4.75% Senior Notes Maturing June 2019 [Member]                  
Debt Instrument [Line Items]                  
Variable interest rate spread         4.75%        
[1] These repurchase agreements had approximately $6.7 million of associated accrued interest payable as of September 30, 2016.