VARIABLE INTEREST ENTITIES - Narrative (Details) - USD ($) $ in Thousands		1 Months Ended	3 Months Ended		6 Months Ended
		Aug. 31, 2017	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021	Dec. 31, 2021		Mar. 31, 2020
Variable Interest Entity [Line Items]
Securitized debt of consolidated VIEs			$ 7,502,483		$ 7,502,483		$ 5,155,633	[1]
Mortgage-backed securities	[2]		59,042,734		59,042,734		63,655,674	[1]
Costs incurred in connection with securitization			36,038	$ 53,526	81,802	$ 101,431
Participations issued			696,944		696,944		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			7,100,000		7,100,000		4,600,000
Costs incurred in connection with securitization			1,800	$ 1,200	5,100	$ 1,800
Contractual principal amount of debt held by third parties			7,800,000		7,800,000		4,600,000
Consolidated VIEs | Consolidation, Eliminations | OBX Trust
Variable Interest Entity [Line Items]
Mortgage-backed securities			998,400		998,400		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 $30.1 million and $44.2 million at June 30, 2022 and December 31, 2021, respectively, of Agency mortgage-backed securities and $971.9 million and $350.4 million at June 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.