SECURED FINANCING - Mortgage Loans Payable (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
Sep. 30, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate	87.00%	85.00%
Utah
Debt Instrument [Line Items]
Interest Rate	3.69%
Commercial Mortgage Loan
Debt Instrument [Line Items]
Mortgage Carrying Value	$ 511,588	$ 309,686
Mortgage Principal	517,503	312,500
Commercial Mortgage Loan \| Utah
Debt Instrument [Line Items]
Mortgage Carrying Value	7,297
Mortgage Principal	7,218
Commercial Mortgage Loan \| Utah \| LIBOR
Debt Instrument [Line Items]
Mortgage Carrying Value	9,691
Mortgage Principal	$ 9,706
Debt instrument, basis spread on variable rate	3.50%
Commercial Mortgage Loan \| Minnesota
Debt Instrument [Line Items]
Mortgage Carrying Value	$ 13,470
Mortgage Principal	$ 13,506
Interest Rate	3.69%
Commercial Mortgage Loan \| Wisconsin
Debt Instrument [Line Items]
Mortgage Carrying Value	$ 7,911
Mortgage Principal	$ 7,932
Interest Rate	3.69%
Commercial Mortgage Loan \| Texas
Debt Instrument [Line Items]
Mortgage Carrying Value	$ 32,317
Mortgage Principal	$ 33,875
Interest Rate	3.28%
Commercial Mortgage Loan \| South Mall \| Tennessee
Debt Instrument [Line Items]
Mortgage Carrying Value	$ 12,319	12,294
Mortgage Principal	$ 12,350	$ 12,350
Interest Rate	4.014%	4.014%
Commercial Mortgage Loan \| 12151 Jefferson \| Virginia
Debt Instrument [Line Items]
Mortgage Carrying Value	$ 96,266	$ 11,019
Mortgage Principal	$ 98,127	$ 11,025
Interest Rate		3.578%
Commercial Mortgage Loan \| Minimum \| 12151 Jefferson \| Virginia
Debt Instrument [Line Items]
Interest Rate	2.34%
Commercial Mortgage Loan \| Maximum \| 12151 Jefferson \| Virginia
Debt Instrument [Line Items]
Interest Rate	4.55%
Commercial Mortgage Loan \| Joint Ventures
Debt Instrument [Line Items]
Mortgage Carrying Value	$ 332,317	$ 286,373
Mortgage Principal	$ 334,789	$ 289,125
Commercial Mortgage Loan \| Joint Ventures \| Minimum
Debt Instrument [Line Items]
Interest Rate	2.75%	4.03%
Commercial Mortgage Loan \| Joint Ventures \| Maximum
Debt Instrument [Line Items]
Interest Rate	4.96%	4.61%

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

No definition available.

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- Definition

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

+ 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(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=64930739&loc=d3e28878-108400

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28551-108399

+ Details

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- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

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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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