VARIABLE INTEREST ENTITIES - Statement of Financial Condition of VIEs Reflected in Consolidated Statements of Financial Condition (Details) - USD ($) $ in Thousands		Jun. 30, 2018	Dec. 31, 2017
ASSETS
Cash and cash equivalents	[1]	$ 1,135,329	$ 706,589	[2]
Commercial real estate debt investments	[3]	2,857,463	3,089,108	[2]
Residential mortgage loans	[4]	1,666,157	1,438,322	[2]
Mortgage servicing rights		599,014	580,860	[2]
Accrued interest receivable		323,769	323,526	[2]
Other derivatives, at fair value		129,680	283,613	[2]
Other assets		475,230	384,117	[2]
Total assets		98,832,997	101,760,050	[2]
Liabilities
Other secured financing		3,760,487	3,837,528	[2]
Accrued interest payable		478,439	253,068	[2]
Accounts payable and other liabilities		68,819	207,770	[2]
Total liabilities		85,059,141	86,888,477	[2]
Consolidated VIEs
ASSETS
Cash and cash equivalents		32,400	42,300
Residential mortgage loans		523,000	478,800
Consolidated VIEs | FREMF Trusts
ASSETS
Cash and cash equivalents		0	0
Commercial real estate debt investments		2,542,413	2,826,357
Residential mortgage loans		0	0
Mortgage servicing rights		0	0
Accrued interest receivable		10,951	10,339
Other derivatives, at fair value			0
Other assets		0	0
Total assets		2,553,364	2,836,696
Liabilities
Securitized debt (non-recourse) at fair value		2,354,380	2,620,952
Other secured financing		0	0
Accrued interest payable		4,572	4,554
Accounts payable and other liabilities		0	0
Total liabilities		2,358,952	2,625,506
Consolidated VIEs | Residential Mortgage Loan Trusts
ASSETS
Cash and cash equivalents		0	0
Commercial real estate debt investments		0	0
Residential mortgage loans		214,694	478,811
Mortgage servicing rights		0	0
Accrued interest receivable		918	1,599
Other derivatives, at fair value			0
Other assets		87	1,418
Total assets		215,699	481,828
Liabilities
Securitized debt (non-recourse) at fair value		117,864	350,819
Other secured financing		0	0
Accrued interest payable		330	931
Accounts payable and other liabilities		140	112
Total liabilities		118,334	351,862
Consolidated VIEs | Mortgage Servicing Rights Silos
ASSETS
Cash and cash equivalents		32,443	42,293
Commercial real estate debt investments		0	0
Residential mortgage loans		37,842	19,667
Mortgage servicing rights		599,014	580,860
Accrued interest receivable		0	0
Other derivatives, at fair value			1
Other assets		33,642	32,354
Total assets		702,941	675,175
Liabilities
Securitized debt (non-recourse) at fair value		0	0
Other secured financing		26,369	10,496
Accrued interest payable		0	0
Accounts payable and other liabilities		1,693	4,856
Total liabilities		$ 28,062	$ 15,352

[1] Includes cash of consolidated Variable Interest Entities (“VIEs”) of $32.4 million and $42.3 million at June 30, 2018 and December 31, 2017, respectively.

[2] Derived from the audited consolidated financial statements at December 31, 2017.

[3] Includes senior securitized commercial mortgage loans of consolidated VIEs carried at fair value of $2.5 billion and $2.8 billion at June 30, 2018 and December 31, 2017, respectively.

[4] Includes securitized residential mortgage loans transferred or pledged to a consolidated VIE carried at fair value of $523.0 million and $478.8 million at June 30, 2018 and December 31, 2017, respectively.