VARIABLE INTEREST ENTITIES - Additional Information (Details) - USD ($)		1 Months Ended	3 Months Ended		6 Months Ended
		Aug. 31, 2017	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Apr. 30, 2019	Feb. 28, 2019	Jan. 31, 2019	Dec. 31, 2018		Oct. 31, 2018	Aug. 31, 2018	Mar. 31, 2018	Jul. 31, 2017
Variable Interest Entity [Line Items]
Residential mortgages loans	[1]		$ 3,546,468,000		$ 3,546,468,000					$ 4,585,975,000	[2]
Other secured financings			4,127,989,000		4,127,989,000					4,183,311,000	[2]
Securitized debt of consolidated VIEs			3,470,168,000		3,470,168,000					3,347,062,000	[2]
Securities (includes pledged assets of $113,624,573 and $87,193,316, respectively) (3)	[3]		119,926,869,000		119,926,869,000					92,623,788,000	[2]
Costs incurred in connection with securitization			78,408,000	$ 63,781,000	162,145,000	$ 126,291,000
Pingora
Variable Interest Entity [Line Items]
Variable interest entity, ownership percentage		100.00%
Consolidated VIEs
Variable Interest Entity [Line Items]
Exposure to obligations of VIEs			2,300,000,000		2,300,000,000
Consolidated VIEs | Consolidation, Eliminations
Variable Interest Entity [Line Items]
Securities (includes pledged assets of $113,624,573 and $87,193,316, respectively) (3)			168,000,000.0		168,000,000.0					224,300,000
Consolidated VIEs | NLY 2019-FL2
Variable Interest Entity [Line Items]
Mortgage loans, unpaid principal balance			795,100,000		795,100,000
Residential mortgages loans								$ 857,300,000
Securitized debt of consolidated VIEs			635,500,000		635,500,000
Contractual principal amount of debt held by third parties			633,900,000		633,900,000
Costs incurred in connection with securitization			8,300,000
Consolidated VIEs | NLY 2019-FL2 | Consolidation, Eliminations
Variable Interest Entity [Line Items]
Securities (includes pledged assets of $113,624,573 and $87,193,316, respectively) (3)			223,800,000		223,800,000
Consolidated VIEs | OBX Trust
Variable Interest Entity [Line Items]
Residential mortgages loans			383,800,000		383,800,000		$ 388,200,000		$ 394,000,000.0			$ 384,000,000.0	$ 383,500,000	$ 327,200,000
Securitized debt of consolidated VIEs			1,600,000,000		1,600,000,000
Contractual principal amount of debt held by third parties			1,500,000,000		1,500,000,000
Costs incurred in connection with securitization			3,000,000.0	$ 0	4,700,000	$ 1,500,000
Consolidated VIEs | OBX Trust | Consolidation, Eliminations
Variable Interest Entity [Line Items]
Securities (includes pledged assets of $113,624,573 and $87,193,316, respectively) (3)			455,200,000		455,200,000
CMBS Securitization Trust | Consolidated VIEs | Collateralized Mortgage Backed Securities
Variable Interest Entity [Line Items]
Commitments to purchase subordinated tranche in securitization trust					94,000,000
Commercial Trusts | Consolidated VIEs
Variable Interest Entity [Line Items]
Mortgage loans, unpaid principal balance			1,300,000,000		1,300,000,000
Residential mortgages loans			0		0					0
Gain (Loss) attributable to instrument- specific credit risk					0
Other secured financings			0		0					0
Commercial Trusts | Consolidated VIEs | Financing Receivables, Equal to Greater than 90 Days Past Due
Variable Interest Entity [Line Items]
Loans 90 days or more past due or on nonaccrual status			0		0
Residential Trusts | Consolidated VIEs
Variable Interest Entity [Line Items]
Residential mortgages loans			0		0					0
Other secured financings			0		0					$ 0
Contractual principal amount of debt held by third parties			75,600,000		75,600,000
Borrower
Variable Interest Entity [Line Items]
Credit facility, maximum borrowing capacity			500,000,000.0		500,000,000.0
Other secured financings			342,800,000		342,800,000
Borrower | Consolidation, Eliminations
Variable Interest Entity [Line Items]
Intercompany receivable			342,800,000		342,800,000
Borrower | Corporate debt held for sale, net
Variable Interest Entity [Line Items]
Transferred loans pledged as collateral for credit facility			651,600,000		651,600,000
Borrower | July 2017 Credit Facility | Consolidated VIEs
Variable Interest Entity [Line Items]
Credit facility, maximum borrowing capacity															$ 250,000,000.0
Borrower | July 2017 Credit Facility | Consolidated VIEs | Corporate debt held for sale, net
Variable Interest Entity [Line Items]
Transferred loans pledged as collateral for credit facility			401,100,000		401,100,000
Other secured financings			$ 127,000,000.0		$ 127,000,000.0
Borrower | January 2019 Credit Facility | Consolidated VIEs
Variable Interest Entity [Line Items]
Credit facility, maximum borrowing capacity									$ 200,000,000.0

[1] ⁽⁴⁾  Includes $119.7 million and $97.5 million of residential mortgage loans held for sale, $41.9 million and $42.2 million of commercial mortgage loans held for sale and $26.9 million and $0 of corporate loans held for sale at June 30, 2019 and December 31, 2018, respectively.

[2] ⁽¹⁾  Derived from the audited consolidated financial statements at December 31, 2018.

[3] ⁽³⁾  Excludes $327.9 million and $83.6 million at June 30, 2019 and December 31, 2018, respectively, of non-Agency mortgage-backed securities and $168.0 million and $224.3 million at June 30, 2019 and December 31, 2018, respectively, of commercial mortgage-backed securities in consolidated VIEs pledged as collateral and eliminated from the Company’s Consolidated Statements of Financial Condition.