MORTGAGE LOAN RECEIVABLES - Additional Information (Details)		12 Months Ended
	Jun. 29, 2017 USD ($) loan	Dec. 31, 2017 USD ($) loan		Dec. 31, 2016 USD ($) loan
Mortgage Loans on Real Estate [Line Items]
Proceeds from sales of mortgage loan receivables	$ 625,700,000
Outstanding Face Amount		$ 3,533,236,000		$ 2,371,827,000
Risk retention requirement, amount	$ 12,900,000
Risk retention requirement, percentage	2.00%
Sold, horizontal interest percentage	3.00%
Controlling classes, percentage	98.00%
Purchase, not recognized for accounting purposes	$ 62,700,000
Gain on sale		26,100,000
Liability for transfers not considered sales		78,800,000
Unamortized discounts included in mortgage loan receivables held for investment, at amortized cost		$ 200,000		600,000
Number of mortgage loans impaired | loan		0
Accrued and unpaid interest receivable		$ 25,875,000	[1]	24,439,000
First mortgage loans
Mortgage Loans on Real Estate [Line Items]
Number of loans | loan	34
Outstanding Face Amount	$ 549,000,000	3,140,788,000		1,843,006,000
Carrying Value	$ 547,700,000
Intercompany loans held-for-investment
Mortgage Loans on Real Estate [Line Items]
Number of loans | loan	23
Outstanding Face Amount	$ 76,700,000
Mortgage loan receivables held for investment, net, at amortized cost
Mortgage Loans on Real Estate [Line Items]
Outstanding Face Amount		3,300,709,000		2,011,309,000
Loans receivable with fixed rates of interest		$ 700,000,000		$ 205,400,000
Percentage of loans receivable with fixed rates of interest		22.00%		10.30%
Loans receivable with variable rates of interest		$ 2,600,000,000		$ 1,800,000,000
Loans receivable with variable rates of interest, percentage		78.00%		89.70%
Number or loans in default | loan		2		2
Loans in default, carrying value		$ 26,900,000
Impairment recorded on defaulted loans		0
Accrued and unpaid interest receivable		4,600,000		$ 3,500,000
Default interest included in accrued and unpaid interest receivable		3,500,000		2,200,000
Mortgage loan receivables held for sale
Mortgage Loans on Real Estate [Line Items]
Outstanding Face Amount		232,527,000		360,518,000
Loans receivable with fixed rates of interest		$ 230,200,000		$ 360,500,000
Percentage of loans receivable with fixed rates of interest		100.00%		100.00%
Loan on non-accrual status
Mortgage Loans on Real Estate [Line Items]
Loans nonaccrual status, amount		$ 0		$ 0

[1] Includes amounts relating to consolidated variable interest entities. See Note 3.