VARIABLE INTEREST ENTITIES - Statement of Financial Condition of VIEs Reflected in Consolidated Statements of Financial Condition (Details) - USD ($) $ in Thousands		Mar. 31, 2018	Dec. 31, 2017
ASSETS
Cash and cash equivalents	[1]	$ 984,275	$ 706,589	[2]
Commercial real estate debt investments	[3]	2,960,323	3,089,108	[2]
Residential mortgage loans	[4]	1,535,685	1,438,322	[2]
Mortgage servicing rights		596,378	580,860	[2]
Accrued interest receivable		326,989	323,526	[2]
Other derivatives, at fair value		161,193	283,613	[2]
Other assets		421,448	384,117	[2]
Total assets		100,382,233	101,760,050	[2]
Liabilities
Other secured financing		3,830,075	3,837,528	[2]
Other derivatives, at fair value		153,103	38,725	[2]
Accrued interest payable		284,696	253,068	[2]
Accounts payable and other liabilities		74,264	207,770	[2]
Total liabilities		86,439,298	86,888,477	[2]
Consolidated VIEs
ASSETS
Cash and cash equivalents		43,200	42,300
Residential mortgage loans		560,200	478,800
Consolidated VIEs | FREMF Trusts
ASSETS
Cash and cash equivalents		0	0
Commercial real estate debt investments		2,695,513	2,826,357
Residential mortgage loans		0	0
Mortgage servicing rights		0	0
Accrued interest receivable		10,762	10,339
Other derivatives, at fair value			0
Other assets		0	0
Total assets		2,706,275	2,836,696
Liabilities
Securitized debt (non-recourse) at fair value		2,497,410	2,620,952
Other secured financing		0	0
Other derivatives, at fair value		0
Accrued interest payable		4,668	4,554
Accounts payable and other liabilities		0	0
Total liabilities		2,502,078	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		229,278	478,811
Mortgage servicing rights		0	0
Accrued interest receivable		901	1,599
Other derivatives, at fair value			0
Other assets		87	1,418
Total assets		230,266	481,828
Liabilities
Securitized debt (non-recourse) at fair value		128,260	350,819
Other secured financing		0	0
Other derivatives, at fair value		0
Accrued interest payable		316	931
Accounts payable and other liabilities		123	112
Total liabilities		128,699	351,862
Consolidated VIEs | Mortgage Servicing Rights Silos
ASSETS
Cash and cash equivalents		43,206	42,293
Commercial real estate debt investments		0	0
Residential mortgage loans		25,206	19,667
Mortgage servicing rights		596,378	580,860
Accrued interest receivable		0	0
Other derivatives, at fair value			1
Other assets		35,486	32,354
Total assets		700,276	675,175
Liabilities
Securitized debt (non-recourse) at fair value		0	0
Other secured financing		16,557	10,496
Other derivatives, at fair value		8
Accrued interest payable		0	0
Accounts payable and other liabilities		2,570	4,856
Total liabilities		$ 19,135	$ 15,352

[1] Includes cash of consolidated Variable Interest Entities (“VIEs”) of $43.2 million and $42.3 million at March 31, 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 $2.7 billion and $2.8 billion at March 31, 2018 and December 31, 2017, respectively.

[4] Includes securitized residential mortgage loans transferred or pledged to a consolidated VIE carried at fair value of $560.2 million and $478.8 million at March 31, 2018 and December 31, 2017, respectively.