VARIABLE INTEREST ENTITIES - Narrative (Details) - USD ($) $ in Thousands		1 Months Ended	3 Months Ended		9 Months Ended
		Aug. 31, 2017	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021	Dec. 31, 2021		Mar. 31, 2020
Variable Interest Entity [Line Items]
Securitized debt of consolidated VIEs			$ 7,844,518		$ 7,844,518		$ 5,155,633	[1]
Mortgage-backed securities	[2]		66,839,353		66,839,353		63,655,674	[1]
Costs incurred in connection with securitization			37,922	$ 43,882	119,724	$ 145,313
Participations issued			745,729		745,729		1,049,066	[1]
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			1,100,000		1,100,000
Consolidated VIEs | OBX Trust
Variable Interest Entity [Line Items]
Securitized debt of consolidated VIEs			7,400,000		7,400,000		4,600,000
Costs incurred in connection with securitization			1,700	$ 2,200	6,800	$ 4,000
Contractual principal amount of debt held by third parties			8,600,000		8,600,000		4,600,000
Consolidated VIEs | Consolidation, Eliminations | OBX Trust
Variable Interest Entity [Line Items]
Mortgage-backed securities			1,000,000		1,000,000		780,800
VIE, Not Primary Beneficiary | Residential mortgage loans
Variable Interest Entity [Line Items]
Participations issued			$ 700,000		$ 700,000		$ 1,000,000
Multifamily | Consolidated VIEs
Variable Interest Entity [Line Items]
Cut-off date principal balance									$ 500,000
Multifamily | Retained Interest | Consolidated VIEs
Variable Interest Entity [Line Items]
Retained interest notional balance									$ 500,000

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

[2] (3)Excludes $27.3 million and $44.2 million at September 30, 2022 and December 31, 2021, respectively, of Agency mortgage-backed securities and $1.0 billion and $350.4 million at September 30, 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.