MORTGAGE LOAN RECEIVABLES - Additional Information (Details)	3 Months Ended
Mar. 31, 2017 USD ($) loan servicing_asset	Mar. 31, 2016 loan	Dec. 31, 2016 USD ($) loan
Mortgage Loans on Real Estate [Line Items]
Number of loans transferred for which Company retains control \| servicing_asset	2
Loans receivable with fixed rates of interest	$ 459,200,000		$ 205,400,000
Percentage of loans receivable with fixed rates of interest	19.90%		10.30%
Unamortized discounts included in mortgage loan receivables held for investment, at amortized cost	$ 500,000		$ 600,000
Number of mortgage loans impaired \| loan	0		0
Accrued and unpaid interest receivable	$ 27,264,000		$ 24,439,000
Mortgage loan receivables held for investment, at amortized cost
Mortgage Loans on Real Estate [Line Items]
Loans receivable with fixed rates of interest	$ 1,800,000,000		$ 1,800,000,000
Percentage of loans receivable with fixed rates of interest	80.10%		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	1,900,000		$ 3,500,000
Default interest included in accrued and unpaid interest receivable	1,800,000		2,200,000
Mortgage loan receivables held for sale
Mortgage Loans on Real Estate [Line Items]
Loans receivable with fixed rates of interest	$ 516,600,000		$ 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]
Number of mortgage loans on non-accrual status \| loan	0	0
Mortgage Loan Financing
Mortgage Loans on Real Estate [Line Items]
Book value of loans transferred for which Company retains control	$ 56,100,000

Financing Receivable Recorded Investment 90 Days Past Due And Still Accruing Number of Contracts

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- Definition

Interest Receivable, Loans Past Due over 90 Days and Still Accruing

+ References

No definition available.

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- Definition

Loans Receivable with Fixed Rates of Interest, Percentage

+ References

No definition available.

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- Definition

Represents the number of mortgage loans individually impaired.

+ References

No definition available.

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- Definition

Transfers Accounted for as Secured Borrowings, Assets, Number

+ References

No definition available.

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- Definition

Principal amount of transferred financial assets in which the transferor has continuing involvement with the assets underlying the transaction. Continuing involvement includes, but is not limited to, servicing, recourse, and restrictions on transferor's interests in transferred financial assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=64830801&loc=d3e107314-111719

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- Definition

Recorded investment in financing receivables that are 90 days or more past due and still accruing.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Recorded Investment
-URI http://asc.fasb.org/extlink&oid=65880944

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-Publisher FASB
-Name Accounting Standards Codification
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-URI http://asc.fasb.org/extlink&oid=66008989&loc=d3e5111-111524

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- Definition

Carrying amount as of the balance sheet date of interest earned but not received. Also called accrued interest or accrued interest receivable.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.8)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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- Definition

Reflects the amount of additional interest income that would have been recorded if impaired or nonperforming loans were instead current, in compliance with their original terms, and outstanding throughout the reporting period or since origination (if held for part of the period).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 40
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=25495931&loc=d3e18794-111554

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- Definition

Amount of loan with fixed rate of interest.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=65884687&loc=d3e4428-111522

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- Definition

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.

+ References

No definition available.

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- Definition

Indicates the number of mortgages under each classification.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 948
-SubTopic 310
-Section S99
-Paragraph 1
-Subparagraph (SX 210.12-29.3)
-URI http://asc.fasb.org/extlink&oid=6589523&loc=d3e617274-123014

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- Definition

Amount of deferred fees paid by borrowers and unamortized costs incurred to originate loans and leases, unamortized loan commitments and loan syndication fees, and premiums over or discounts from face amounts of loans that are being amortized into income as an adjustment to yield. Excludes amounts for loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6378536&loc=d3e10092-111533

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