FAIR VALUE MEASUREMENTS - Real Estate And Other Securities Valuation Methodology and Results (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2023 USD ($) source	Dec. 31, 2022 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Outstanding Face Amount	$ 27,610,692	$ 25,370,934
Amortized Cost Basis	9,611,416	8,237,819
Real estate and other securities	$ 9,757,664	8,289,277
Number of broker quotation sources | source	2
Multiple Quotes
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Real estate and other securities	$ 9,523,776	8,289,263
Single Quote
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Real estate and other securities	233,888	14
Agency
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Outstanding Face Amount	8,590,260	7,463,522
Amortized Cost Basis	8,417,025	7,290,473
Agency | Level 2
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Real estate and other securities	8,533,130	7,338,417
Agency | Level 2 | Multiple Quotes
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Real estate and other securities	8,533,130	7,338,417
Agency | Level 2 | Single Quote
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Real estate and other securities	0	0
Non-Agency
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Outstanding Face Amount	19,020,432	17,907,412
Amortized Cost Basis	$ 1,194,391	$ 947,346
Percent of securities	46.80%	50.40%
Fair Value	$ 572,604	$ 479,406
Non-Agency | Minimum | Discount Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Discount Rate	0.041	0.035
Non-Agency | Minimum | Prepayment Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Discount Rate	0.000	0.000
Non-Agency | Minimum | CDR
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Discount Rate	0.000	0.000
Non-Agency | Minimum | Loss Severity
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Discount Rate	0.000	0.000
Non-Agency | Maximum | Discount Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Discount Rate	0.335	0.150
Non-Agency | Maximum | Prepayment Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Discount Rate	0.200	0.250
Non-Agency | Maximum | CDR
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Discount Rate	0.080	0.120
Non-Agency | Maximum | Loss Severity
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Discount Rate	0.450	0.880
Non-Agency | Weighted Average | Discount Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Discount Rate	0.062	0.065
Non-Agency | Weighted Average | Prepayment Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Discount Rate	0.113	0.111
Non-Agency | Weighted Average | CDR
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Discount Rate	0.011	0.006
Non-Agency | Weighted Average | Loss Severity
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Discount Rate	0.206	0.103
Non-Agency | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Real estate and other securities	$ 1,224,534	$ 950,860
Non-Agency | Level 3 | Multiple Quotes
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Real estate and other securities	990,646	950,846
Non-Agency | Level 3 | Single Quote
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Real estate and other securities	$ 233,888	$ 14