VARIABLE INTEREST ENTITIES - Narrative (Details) - USD ($)		1 Months Ended	3 Months Ended
		Aug. 31, 2017	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021		Mar. 31, 2020
Variable Interest Entity [Line Items]
Principal receivable	[1]		$ 3,617,818,000		$ 4,242,043,000	[2]
Securitized debt of consolidated VIEs			6,711,953,000		5,155,633,000	[2]
Mortgage-backed securities	[3]		60,727,637,000		63,655,674,000	[2]
Costs incurred in connection with securitization			45,764,000	$ 47,905,000
Other secured financing			914,255,000		903,255,000	[2]
Participations issued			775,432,000		1,049,066,000	[2]
MSR Silo
Variable Interest Entity [Line Items]
Variable interest entity, ownership percentage		100.00%
Consolidated VIEs
Variable Interest Entity [Line Items]
Exposure to obligations of VIEs			2,500,000,000
Loans transferred for cash			0	15,100,000
Consolidated VIEs | OBX Trust
Variable Interest Entity [Line Items]
Contractual principal amount of debt held by third parties			6,500,000,000		4,600,000,000
Securitized debt of consolidated VIEs			6,200,000,000		4,600,000,000
Costs incurred in connection with securitization			3,400,000	$ 700,000
Consolidated VIEs | Consolidation, Eliminations | OBX Trust
Variable Interest Entity [Line Items]
Mortgage-backed securities			892,500,000		780,800,000
Consolidated VIEs | Borrower | June 2016 Credit Facility
Variable Interest Entity [Line Items]
Credit facility, maximum borrowing capacity			675,000,000		675,000,000
Other secured financing			455,500,000		433,300,000
Consolidated VIEs | Borrower | June 2016 Credit Facility | Corporate Loans
Variable Interest Entity [Line Items]
Transferred loans pledged as collateral for credit facility			716,400,000		692,600,000
Consolidated VIEs | Borrower | July 2017 Credit Facility
Variable Interest Entity [Line Items]
Credit facility, maximum borrowing capacity			234,200,000		400,000,000
Consolidated VIEs | Borrower | July 2017 Credit Facility | Corporate Loans
Variable Interest Entity [Line Items]
Transferred loans pledged as collateral for credit facility			396,600,000		402,900,000
Other secured financing			234,200,000		238,200,000
Consolidated VIEs | Borrower | January 2019 Credit Facility
Variable Interest Entity [Line Items]
Credit facility, maximum borrowing capacity			400,000,000		400,000,000
Consolidated VIEs | Borrower | January 2019 Credit Facility | Corporate Loans
Variable Interest Entity [Line Items]
Transferred loans pledged as collateral for credit facility			362,400,000		368,000,000
Other secured financing			224,600,000		231,800,000
Consolidated VIEs | Borrower | Consolidation, Eliminations | June 2016 Credit Facility
Variable Interest Entity [Line Items]
Principal receivable			455,500,000		433,300,000
VIE, Not Primary Beneficiary | Residential mortgage loans
Variable Interest Entity [Line Items]
Participations issued			$ 800,000,000		$ 1,000,000,000
Multifamily | Consolidated VIEs
Variable Interest Entity [Line Items]
Cut-off date principal balance							$ 500,000,000
Multifamily | Retained Interest | Consolidated VIEs
Variable Interest Entity [Line Items]
Retained interest notional balance							$ 500,000,000

[1] (4)Includes $1.9 million and $2.3 million of residential mortgage loans held for sale at March 31, 2022 and December 31, 2021, respectively.

[2] (1)Derived from the audited consolidated financial statements at December 31, 2021.

[3] (3)Excludes $38.5 million and $44.2 million at March 31, 2022 and December 31, 2021, respectively, of Agency mortgage-backed securities and $709.0 million and $350.4 million at March 31, 2022 and December 31, 2021, respectively, of non-Agency mortgage-backed securities in consolidated VIEs pledged as collateral and eliminated from the Company’s Consolidated Statements of Financial Condition.