VARIABLE INTEREST ENTITIES - Additional Information (Details)	1 Months Ended				3 Months Ended		12 Months Ended
	Aug. 31, 2017	Feb. 29, 2016 USD ($) loan	Apr. 30, 2015 USD ($) loan	Feb. 28, 2015 USD ($) loan	Dec. 31, 2017 USD ($)		Dec. 31, 2017 USD ($)		Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Jul. 31, 2017 USD ($)	Jun. 30, 2016 USD ($)
Variable Interest Entity [Line Items]
Payments to purchase mortgage loans							$ 289,979,000		$ 99,590,000	$ 0
Face value					$ 1,033,158,000		1,033,158,000
Exposure to obligations of VIEs									205,400,000
Gain (loss) recognized upon initial consolidation					7,100,000
Contractual principal amount of residential mortgage trust debt							349,220,000		654,117,000
Other secured financings					3,837,528,000	[1]	3,837,528,000	[1]	3,884,708,000
Borrower
Variable Interest Entity [Line Items]
Other secured financings					138,200,000		138,200,000
Borrower | Corporate Debt Securities
Variable Interest Entity [Line Items]
Transferred loans pledged as collateral for credit facility					415,600,000		415,600,000
Pingora
Variable Interest Entity [Line Items]
Variable interest entity, ownership percentage	100.00%
Borrower
Variable Interest Entity [Line Items]
Credit facility, maximum borrowing capacity												$ 300,000,000
Borrower | Consolidation, Eliminations
Variable Interest Entity [Line Items]
Intercompany receivable					138,200,000		138,200,000
Freddie Mac | FREMF 2015-KLSF | Floating Rate Multifamily Mortgage Loans
Variable Interest Entity [Line Items]
Number of loans in the underlying portfolio (loan) | loan				11
Face value				$ 1,400,000,000
Freddie Mac | FREMF 2015-KF07 | Floating Rate Multifamily Mortgage Loans
Variable Interest Entity [Line Items]
Number of loans in the underlying portfolio (loan) | loan			40
Face value			$ 1,200,000,000
Freddie Mac | FREMF 2016-KLH1 | Floating Rate Multifamily Mortgage Loans
Variable Interest Entity [Line Items]
Number of loans in the underlying portfolio (loan) | loan		28
Face value		$ 1,500,000,000
Consolidated VIEs
Variable Interest Entity [Line Items]
Exposure to obligations of VIEs					1,000,000,000		1,000,000,000
Gain (loss) recognized upon initial consolidation									0
Debt issue costs expensed									800,000
Consolidated VIEs | FREMF Trusts
Variable Interest Entity [Line Items]
Mortgage loans, unpaid principal balance					2,800,000,000		2,800,000,000
Gain (Loss) attributable to instrument- specific credit risk							0
Other secured financings					0		0		0
Consolidated VIEs | FREMF Trusts | 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
Consolidated VIEs | Residential Mortgage Loan Trusts
Variable Interest Entity [Line Items]
Mortgage loans, unpaid principal balance					312,900,000		312,900,000
Contractual principal amount of residential mortgage trust debt							35,800,000
Other secured financings					0		0		$ 0
Consolidated VIEs | Freddie Mac | FREMF 2015-KLSF
Variable Interest Entity [Line Items]
Payments to purchase mortgage loans				$ 102,100,000
Variable interest entity, consolidated, carrying amount, assets					574,100,000		574,100,000
Variable interest entity, consolidated, carrying amount, liabilities					532,200,000		532,200,000
Consolidated VIEs | Freddie Mac | FREMF 2015-KF07
Variable Interest Entity [Line Items]
Payments to purchase mortgage loans			$ 89,400,000
Variable interest entity, consolidated, carrying amount, assets					712,300,000		712,300,000
Variable interest entity, consolidated, carrying amount, liabilities					661,700,000		661,700,000
Consolidated VIEs | Freddie Mac | FREMF 2016-KLH1
Variable Interest Entity [Line Items]
Payments to purchase mortgage loans		107,600,000
Face value		112,000,000
Variable interest entity, consolidated, carrying amount, assets					1,500,000,000		1,500,000,000
Variable interest entity, consolidated, carrying amount, liabilities					1,400,000,000		1,400,000,000
Discounted value		$ 4,400,000
July 2017 Credit Facility | Consolidated VIEs | Borrower
Variable Interest Entity [Line Items]
Credit facility, maximum borrowing capacity											$ 150,000,000
July 2017 Credit Facility | Consolidated VIEs | Borrower | Corporate Debt Securities
Variable Interest Entity [Line Items]
Transferred loans pledged as collateral for credit facility					184,500,000		184,500,000
Other secured financings					$ 100,500,000		$ 100,500,000

[1] As a result of a change to a clearing organization’s rulebook effective January 3, 2017, beginning with the first quarter 2017 and in subsequent periods the Company is presenting the fair value of centrally cleared interest rate swaps net of variation margin pledged under such transactions. The variation margin was previously reported under cash and cash equivalents and is currently reported as a reduction to interest rate swaps, at fair value. Balances reported prior to the effective date will not be adjusted.