DEBT OBLIGATIONS, NET - Schedule of Company's Debt Obligations (Details)				12 Months Ended
	Aug. 03, 2016 USD ($) Extension	Apr. 19, 2016 Extension	Oct. 25, 2015 USD ($) Extension	Dec. 31, 2016 USD ($) Extension	Dec. 31, 2015 USD ($) Extension	Jul. 01, 2016 USD ($)	Jun. 28, 2016 USD ($)	Aug. 14, 2015 USD ($) Extension	Apr. 10, 2015 USD ($)	Feb. 19, 2015 Extension
Assets Sold under Agreements to Repurchase [Line Items]
Debt obligations outstanding				$ 1,107,185,000	$ 1,260,755,000
Debt obligations, net				3,942,138,000	4,274,723,000
Carrying Amount of Collateral				0	0
Unamortized debt issuance costs				(4,025,000)
Committed Loan Repurchase Facilities
Assets Sold under Agreements to Repurchase [Line Items]
Committed amount on master repurchase agreement				1,650,000,000	1,485,000,000
Debt obligations outstanding				567,163,000	704,149,000
Committed but Unfunded				1,082,837,000	780,851,000
Carrying Amount of Collateral				961,791,000	1,101,593,000
Securities Sold under Agreements to Repurchase, Fair Value of Collateral				965,888,000	$ 1,176,417,000
Committed Loan Repurchase Facilities | 10/30/2018
Assets Sold under Agreements to Repurchase [Line Items]
Committed amount on master repurchase agreement				600,000,000
Debt obligations outstanding				183,604,000
Committed but Unfunded				416,396,000
Carrying Amount of Collateral				292,628,000
Securities Sold under Agreements to Repurchase, Fair Value of Collateral				$ 293,618,000
Number of extension maturity periods | Extension				3
Length of extension options				12 months	1 year
Committed Loan Repurchase Facilities | 10/30/2018 | Minimum
Assets Sold under Agreements to Repurchase [Line Items]
Interest Rate(s) (as a percent)				2.45%
Committed Loan Repurchase Facilities | 10/30/2018 | Maximum
Assets Sold under Agreements to Repurchase [Line Items]
Interest Rate(s) (as a percent)				3.27%
Committed Loan Repurchase Facilities | 5/24/2017
Assets Sold under Agreements to Repurchase [Line Items]
Committed amount on master repurchase agreement				$ 450,000,000
Debt obligations outstanding				184,158,000
Committed but Unfunded				265,842,000
Carrying Amount of Collateral				286,848,000
Securities Sold under Agreements to Repurchase, Fair Value of Collateral				$ 288,267,000
Number of extension maturity periods | Extension		2		3
Length of extension options		1 year		12 months
Committed Loan Repurchase Facilities | 5/24/2017 | Minimum
Assets Sold under Agreements to Repurchase [Line Items]
Interest Rate(s) (as a percent)				2.95%
Committed Loan Repurchase Facilities | 5/24/2017 | Maximum
Assets Sold under Agreements to Repurchase [Line Items]
Interest Rate(s) (as a percent)				3.70%
Committed Loan Repurchase Facilities | 4/9/2017
Assets Sold under Agreements to Repurchase [Line Items]
Committed amount on master repurchase agreement				$ 400,000,000					$ 400,000,000.0
Debt obligations outstanding				100,979,000
Committed but Unfunded				299,021,000
Carrying Amount of Collateral				235,878,000
Securities Sold under Agreements to Repurchase, Fair Value of Collateral				$ 236,696,000
Number of extension maturity periods | Extension				2
Length of extension options				364 days
Committed Loan Repurchase Facilities | 4/9/2017 | Minimum
Assets Sold under Agreements to Repurchase [Line Items]
Interest Rate(s) (as a percent)				2.95%
Committed Loan Repurchase Facilities | 4/9/2017 | Maximum
Assets Sold under Agreements to Repurchase [Line Items]
Interest Rate(s) (as a percent)				3.99%
Committed Loan Repurchase Facilities | 6/28/2019
Assets Sold under Agreements to Repurchase [Line Items]
Committed amount on master repurchase agreement				$ 100,000,000			$ 100,000,000.0
Debt obligations outstanding				27,132,000
Committed but Unfunded				72,868,000
Carrying Amount of Collateral				36,166,000
Securities Sold under Agreements to Repurchase, Fair Value of Collateral				$ 36,410,000
Committed Loan Repurchase Facilities | 6/28/2019 | Minimum
Assets Sold under Agreements to Repurchase [Line Items]
Interest Rate(s) (as a percent)				2.90%
Committed Loan Repurchase Facilities | 6/28/2019 | Maximum
Assets Sold under Agreements to Repurchase [Line Items]
Interest Rate(s) (as a percent)				3.13%
Committed Loan Repurchase Facilities | 8/2/2019
Assets Sold under Agreements to Repurchase [Line Items]
Committed amount on master repurchase agreement	$ 100,000,000.0			$ 100,000,000
Debt obligations outstanding				71,290,000
Committed but Unfunded				28,710,000
Carrying Amount of Collateral				110,271,000
Securities Sold under Agreements to Repurchase, Fair Value of Collateral				$ 110,897,000
Number of extension maturity periods | Extension	1			1
Length of extension options	12 months			12 months
Number of additional extension maturity periods | Extension	2			2
Length of additional extension maturity periods	6 months			6 months
Committed Loan Repurchase Facilities | 8/2/2019 | Minimum
Assets Sold under Agreements to Repurchase [Line Items]
Interest Rate(s) (as a percent)				2.93%
Committed Loan Repurchase Facilities | 8/2/2019 | Maximum
Assets Sold under Agreements to Repurchase [Line Items]
Interest Rate(s) (as a percent)				3.68%
Committed Loan Repurchase Facilities | 10/30/2016
Assets Sold under Agreements to Repurchase [Line Items]
Committed amount on master repurchase agreement					$ 600,000,000			$ 600,000,000.0
Debt obligations outstanding					229,533,000
Committed but Unfunded					370,467,000
Carrying Amount of Collateral					364,978,000
Securities Sold under Agreements to Repurchase, Fair Value of Collateral					$ 366,676,000
Number of extension maturity periods | Extension					2			1
Length of extension options					12 months
Committed Loan Repurchase Facilities | 10/30/2016 | Minimum
Assets Sold under Agreements to Repurchase [Line Items]
Interest Rate(s) (as a percent)					2.08%
Committed Loan Repurchase Facilities | 10/30/2016 | Maximum
Assets Sold under Agreements to Repurchase [Line Items]
Interest Rate(s) (as a percent)					2.93%
Committed Loan Repurchase Facilities | 4/10/2016
Assets Sold under Agreements to Repurchase [Line Items]
Committed amount on master repurchase agreement					$ 400,000,000
Debt obligations outstanding					204,262,000
Committed but Unfunded					195,738,000
Carrying Amount of Collateral					299,714,000
Securities Sold under Agreements to Repurchase, Fair Value of Collateral					$ 342,307,000
Number of extension maturity periods | Extension					2
Length of extension options					364 days
Committed Loan Repurchase Facilities | 4/10/2016 | Minimum
Assets Sold under Agreements to Repurchase [Line Items]
Interest Rate(s) (as a percent)					2.44%
Committed Loan Repurchase Facilities | 4/10/2016 | Maximum
Assets Sold under Agreements to Repurchase [Line Items]
Interest Rate(s) (as a percent)					4.33%
Committed Loan Repurchase Facilities | 4/10/2016 | Consolidated Subsidiaries
Assets Sold under Agreements to Repurchase [Line Items]
Debt obligations outstanding					$ 36,500,000
Committed Loan Repurchase Facilities | 5/24/2016
Assets Sold under Agreements to Repurchase [Line Items]
Committed amount on master repurchase agreement					450,000,000
Debt obligations outstanding					269,779,000
Committed but Unfunded					180,221,000
Carrying Amount of Collateral					436,901,000
Securities Sold under Agreements to Repurchase, Fair Value of Collateral					$ 466,640,000
Number of extension maturity periods | Extension					2
Length of extension options					12 months
Committed Loan Repurchase Facilities | 5/24/2016 | Minimum
Assets Sold under Agreements to Repurchase [Line Items]
Interest Rate(s) (as a percent)					2.58%
Committed Loan Repurchase Facilities | 5/24/2016 | Maximum
Assets Sold under Agreements to Repurchase [Line Items]
Interest Rate(s) (as a percent)					4.33%
Committed Loan Repurchase Facilities | 5/24/2016 | Consolidated Subsidiaries
Assets Sold under Agreements to Repurchase [Line Items]
Debt obligations outstanding					$ 28,200,000
Committed Loan Repurchase Facilities | 10/24/2016
Assets Sold under Agreements to Repurchase [Line Items]
Committed amount on master repurchase agreement			$ 35,000,000.0		35,000,000
Debt obligations outstanding					575,000
Committed but Unfunded					$ 34,425,000
Interest Rate(s) (as a percent)					3.02%
Carrying Amount of Collateral					$ 0
Securities Sold under Agreements to Repurchase, Fair Value of Collateral					$ 794,000
Number of extension maturity periods | Extension			2		2
Length of extension options			6 months		6 months
Committed Loan Repurchase Facilities | 10/24/2016 | Consolidated Subsidiaries
Assets Sold under Agreements to Repurchase [Line Items]
Debt obligations outstanding					$ 800,000
Committed Securities Repurchase Facility
Assets Sold under Agreements to Repurchase [Line Items]
Committed amount on master repurchase agreement				$ 400,000,000.0
Number of extension maturity periods | Extension										1
Committed Securities Repurchase Facility | 10/31/2016
Assets Sold under Agreements to Repurchase [Line Items]
Committed amount on master repurchase agreement					300,000,000
Debt obligations outstanding					161,887,000
Committed but Unfunded					138,113,000
Carrying Amount of Collateral					193,530,000
Securities Sold under Agreements to Repurchase, Fair Value of Collateral					$ 193,530,000
Committed Securities Repurchase Facility | 10/31/2016 | Minimum
Assets Sold under Agreements to Repurchase [Line Items]
Interest Rate(s) (as a percent)					0.88%
Committed Securities Repurchase Facility | 10/31/2016 | Maximum
Assets Sold under Agreements to Repurchase [Line Items]
Interest Rate(s) (as a percent)					1.34%
Committed Securities Repurchase Facility | 7/1/2018
Assets Sold under Agreements to Repurchase [Line Items]
Committed amount on master repurchase agreement				400,000,000		$ 400,000,000.0
Debt obligations outstanding				228,317,000
Committed but Unfunded				171,683,000
Carrying Amount of Collateral				272,402,000
Securities Sold under Agreements to Repurchase, Fair Value of Collateral				$ 272,402,000
Committed Securities Repurchase Facility | 7/1/2018 | Minimum
Assets Sold under Agreements to Repurchase [Line Items]
Interest Rate(s) (as a percent)				1.00%
Committed Securities Repurchase Facility | 7/1/2018 | Maximum
Assets Sold under Agreements to Repurchase [Line Items]
Interest Rate(s) (as a percent)				2.59%
Uncommitted Securities Repurchase Facilities | 1/2016
Assets Sold under Agreements to Repurchase [Line Items]
Debt obligations outstanding					$ 394,719,000
Carrying Amount of Collateral					458,615,000
Securities Sold under Agreements to Repurchase, Fair Value of Collateral					$ 458,615,000
Uncommitted Securities Repurchase Facilities | 1/2016 | Minimum
Assets Sold under Agreements to Repurchase [Line Items]
Interest Rate(s) (as a percent)					0.73%
Uncommitted Securities Repurchase Facilities | 1/2016 | Maximum
Assets Sold under Agreements to Repurchase [Line Items]
Interest Rate(s) (as a percent)					2.02%
Uncommitted Securities Repurchase Facilities | Various Dates
Assets Sold under Agreements to Repurchase [Line Items]
Debt obligations outstanding				$ 311,705,000
Carrying Amount of Collateral				368,638,000
Securities Sold under Agreements to Repurchase, Fair Value of Collateral				$ 368,638,000
Uncommitted Securities Repurchase Facilities | Various Dates | Minimum
Assets Sold under Agreements to Repurchase [Line Items]
Interest Rate(s) (as a percent)				1.00%
Uncommitted Securities Repurchase Facilities | Various Dates | Maximum
Assets Sold under Agreements to Repurchase [Line Items]
Interest Rate(s) (as a percent)				2.41%
Total Repurchase Facilities
Assets Sold under Agreements to Repurchase [Line Items]
Committed amount on master repurchase agreement				$ 2,050,000,000	$ 1,785,000,000
Debt obligations outstanding				1,107,185,000	1,260,755,000
Committed but Unfunded				1,254,520,000	918,964,000
Carrying Amount of Collateral				1,602,831,000	1,753,738,000
Securities Sold under Agreements to Repurchase, Fair Value of Collateral				1,606,928,000	1,828,562,000
Borrowing Under Credit Agreement | 1/24/2016
Assets Sold under Agreements to Repurchase [Line Items]
Committed amount on master repurchase agreement					50,000,000
Debt obligations outstanding					0
Committed but Unfunded					50,000,000
Carrying Amount of Collateral					0
Securities Sold under Agreements to Repurchase, Fair Value of Collateral					0
Revolving Credit Facility | 2/11/2017
Assets Sold under Agreements to Repurchase [Line Items]
Committed amount on master repurchase agreement				143,000,000	75,000,000
Debt obligations outstanding				25,000,000	0
Committed but Unfunded				$ 118,000,000	$ 75,000,000
Interest Rate(s) (as a percent)				3.16%
Number of extension maturity periods | Extension					2
Length of extension options					12 months
Mortgage Loan Financing | 2/11/2017
Assets Sold under Agreements to Repurchase [Line Items]
Number of extension maturity periods | Extension				2
Length of extension options				12 months
Mortgage Loan Financing | Various Dates
Assets Sold under Agreements to Repurchase [Line Items]
Committed amount on master repurchase agreement				$ 590,106,000	$ 544,663,000
Debt obligations outstanding				590,106,000	544,663,000
Committed but Unfunded				0	0
Carrying Amount of Collateral				757,468,000	711,090,000
Securities Sold under Agreements to Repurchase, Fair Value of Collateral				$ 875,160,000	$ 788,369,000
Mortgage Loan Financing | Various Dates | Minimum
Assets Sold under Agreements to Repurchase [Line Items]
Interest Rate(s) (as a percent)				4.25%	4.25%
Mortgage Loan Financing | Various Dates | Maximum
Assets Sold under Agreements to Repurchase [Line Items]
Interest Rate(s) (as a percent)				6.75%	6.75%
Borrowings from the FHLB | Various Dates
Assets Sold under Agreements to Repurchase [Line Items]
Committed amount on master repurchase agreement				$ 1,998,931,000	$ 2,237,113,000
Debt obligations outstanding				1,660,000,000	1,856,700,000
Committed but Unfunded				338,931,000	380,413,000
Carrying Amount of Collateral				2,162,779,000	2,317,534,000
Securities Sold under Agreements to Repurchase, Fair Value of Collateral				$ 2,167,017,000	$ 2,323,765,000
Borrowings from the FHLB | Various Dates | Minimum
Assets Sold under Agreements to Repurchase [Line Items]
Interest Rate(s) (as a percent)				0.43%	0.28%
Borrowings from the FHLB | Various Dates | Maximum
Assets Sold under Agreements to Repurchase [Line Items]
Interest Rate(s) (as a percent)				2.74%	2.74%
Senior Unsecured Notes | Various Dates
Assets Sold under Agreements to Repurchase [Line Items]
Debt issued				$ 563,872,000	$ 619,555,000
Senior unsecured notes				559,847,000	612,605,000
Committed but Unfunded				0	0
Unamortized debt issuance costs				$ (4,000,000.0)	$ (6,900,000)
Senior Unsecured Notes | Various Dates | Minimum
Assets Sold under Agreements to Repurchase [Line Items]
Stated interest rate on debt instrument (as a percent)				5.875%	5.875%
Senior Unsecured Notes | Various Dates | Maximum
Assets Sold under Agreements to Repurchase [Line Items]
Stated interest rate on debt instrument (as a percent)				7.375%	7.375%
Total Debt Obligations
Assets Sold under Agreements to Repurchase [Line Items]
Debt issued				$ 5,345,909,000	$ 5,311,331,000
Debt obligations, net				3,942,138,000	4,274,723,000
Committed but Unfunded				1,711,451,000	1,424,377,000
Carrying Amount of Collateral				4,523,078,000	4,782,362,000
Securities Sold under Agreements to Repurchase, Fair Value of Collateral				$ 4,649,105,000	$ 4,940,696,000