MORTGAGE LOAN RECEIVABLES - Schedule of Mortgage Loans (Details) $ in Thousands			9 Months Ended	12 Months Ended
Sep. 30, 2017 USD ($) loan	Jun. 29, 2017 USD ($) loan	Sep. 30, 2017 USD ($)	Dec. 31, 2016 USD ($)
Mortgage Loans on Real Estate [Line Items]
Outstanding Face Amount	$ 3,989,046		$ 3,989,046	$ 2,371,827
Provision for loan losses	(4,000)		(4,000)	(4,000)
Carrying Value	3,964,426		$ 3,964,426	$ 2,353,977
Weighted Average Yield (as a percent)			5.70%	6.73%
Remaining Maturity (years)			3 years 7 months 17 days	2 years 1 month 6 days
Mortgage loans held by consolidated subsidiaries
Mortgage Loans on Real Estate [Line Items]
Outstanding Face Amount	2,862,739		$ 2,862,739	$ 2,011,309
Carrying Value	2,846,940		$ 2,846,940	$ 2,000,095
Weighted Average Yield (as a percent)			7.06%	7.17%
Remaining Maturity (years)			1 year 8 months 15 days	1 year 7 months 28 days
Mortgage loans transferred but not considered sold
Mortgage Loans on Real Estate [Line Items]
Outstanding Face Amount	600,222		$ 600,222	$ 0
Carrying Value	598,525		$ 598,525
Weighted Average Yield (as a percent)			4.92%
Remaining Maturity (years)			8 years 4 months 17 days
Mortgage loan receivables held for investment, net, at amortized cost
Mortgage Loans on Real Estate [Line Items]
Outstanding Face Amount	3,462,961		$ 3,462,961	2,011,309
Carrying Value	3,441,465		3,441,465	1,996,095
Mortgage loan receivables held for sale
Mortgage Loans on Real Estate [Line Items]
Outstanding Face Amount	526,085		526,085	360,518
Carrying Value	522,961		$ 522,961	$ 357,882
Weighted Average Yield (as a percent)			4.79%	4.20%
Remaining Maturity (years)			8 years 7 months 17 days	4 years 6 months 18 days
First mortgage loan, held for investment
Mortgage Loans on Real Estate [Line Items]
Outstanding Face Amount	2,703,936	$ 549,000	$ 2,703,936	$ 1,843,006
Carrying Value	$ 546,700	$ 547,700	546,700
Number of loans \| loan	34	34
Mortgage Loans On Real Estate Face Amount Of Mortgages Balance Sheet Date, Transfered Not Sold	$ 548,000		$ 548,000
Non-Controlling loan interest
Mortgage Loans on Real Estate [Line Items]
Outstanding Face Amount		$ 52,300
Carrying Value		$ 51,800
Number of loans \| loan		1

Amount of the contractual principal due as of the balance sheet date of the mortgage loan (face amount).

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- Definition

Mortgage Loans On Real Estate Face Amount Of Mortgages Balance Sheet Date, Transfered Not Sold

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Represents the remaining maturity period of mortgage loans.

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Mortgage Loans on Real Estate, Gross, Commercial and Consumer, Net

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- Definition

Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

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- Definition

The balance represents the amount of loans that are secured by real estate mortgages, offset by the reserve to cover probable credit losses on the loan portfolio.

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The stated interest rate on the mortgage loan receivable or the weighted average interest rate on a group of loans.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Indicates the number of mortgages under each classification.

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