FAIR VALUE MEASUREMENTS - Securities Valuation Methodology and Results (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2022 USD ($) source	Dec. 31, 2021 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Outstanding Face Amount	$ 26,609,422
Amortized Cost Basis	10,021,436
Real estate and other securities	$ 9,437,008	$ 9,396,539
Number of broker quotation sources | source	2
Percent of securities	57.40%
Multiple Quotes
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Real estate and other securities	$ 9,436,993
Single Quote
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Real estate and other securities	15
RMBS Designated as AFS
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Outstanding Face Amount	9,098,824
Amortized Cost Basis	9,082,503
RMBS Designated as AFS | Level 2
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Real estate and other securities	8,497,960
RMBS Designated as AFS | Level 2 | Multiple Quotes
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Real estate and other securities	8,497,960
RMBS Designated as AFS | Level 2 | Single Quote
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Real estate and other securities	0
Non-Agency RMBS
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Outstanding Face Amount	17,510,598
Amortized Cost Basis	938,933
Fair Value	538,658
Non-Agency RMBS | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Real estate and other securities	939,048
Non-Agency RMBS | Level 3 | Multiple Quotes
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Real estate and other securities	939,033
Non-Agency RMBS | Level 3 | Single Quote
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Real estate and other securities	$ 15
Non-Agency RMBS | Minimum | Discount Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Non agency RMBS, measurement input	0.040
Non-Agency RMBS | Minimum | Prepayment Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Non agency RMBS, measurement input	0.000
Non-Agency RMBS | Minimum | Delinquency
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Non agency RMBS, measurement input	0.000
Non-Agency RMBS | Minimum | Loss Severity
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Non agency RMBS, measurement input	0.000
Non-Agency RMBS | Maximum | Discount Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Non agency RMBS, measurement input	0.169
Non-Agency RMBS | Maximum | Prepayment Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Non agency RMBS, measurement input	0.250
Non-Agency RMBS | Maximum | Delinquency
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Non agency RMBS, measurement input	0.120
Non-Agency RMBS | Maximum | Loss Severity
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Non agency RMBS, measurement input	0.880
Non-Agency RMBS | Weighted Average | Discount Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Non agency RMBS, measurement input	0.060
Non-Agency RMBS | Weighted Average | Prepayment Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Non agency RMBS, measurement input	0.046
Non-Agency RMBS | Weighted Average | Delinquency
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Non agency RMBS, measurement input	0.011
Non-Agency RMBS | Weighted Average | Loss Severity
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Non agency RMBS, measurement input	0.214