FAIR VALUE MEASUREMENTS - Securities Valuation Methodology and Results (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2022 USD ($) source	Dec. 31, 2021 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Outstanding Face Amount	$ 25,301,502
Amortized Cost Basis	9,141,163
Real estate and other securities	$ 7,988,802	$ 9,396,539
Number of broker quotation sources | source	2
Percent of securities	53.00%
Multiple Quotes
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Real estate and other securities	$ 7,988,802
Single Quote
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Real estate and other securities	0
RMBS Designated as AFS
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Outstanding Face Amount	7,996,986
Amortized Cost Basis	8,219,305
RMBS Designated as AFS | Level 2
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Real estate and other securities	7,064,068
RMBS Designated as AFS | Level 2 | Multiple Quotes
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Real estate and other securities	7,064,068
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	17,304,516
Amortized Cost Basis	921,858
Fair Value	489,732
Non-Agency RMBS | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Real estate and other securities	924,734
Non-Agency RMBS | Level 3 | Multiple Quotes
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Real estate and other securities	924,734
Non-Agency RMBS | Level 3 | Single Quote
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Real estate and other securities	$ 0
Non-Agency RMBS | Minimum | Discount Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Non agency RMBS, measurement input	0.035
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	0.150
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	0.052
Non-Agency RMBS | Weighted Average | Prepayment Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Non agency RMBS, measurement input	0.089
Non-Agency RMBS | Weighted Average | Delinquency
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Non agency RMBS, measurement input	0.015
Non-Agency RMBS | Weighted Average | Loss Severity
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Non agency RMBS, measurement input	0.263