SECURED FINANCING - Mortgage Loans Payable (Details) - USD ($)	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Variable interest rate	92.00%	88.00%
Commercial Mortgage Loans
Debt Instrument [Line Items]
Mortgage carrying value	$ 485,005,000	$ 511,056,000
Mortgage principal	490,631,000	516,834,000
Joint Ventures \| Commercial Mortgage Loans
Debt Instrument [Line Items]
Mortgage carrying value	316,566,000	316,275,000
Mortgage principal	$ 318,562,000	$ 318,664,000
Joint Ventures \| Commercial Mortgage Loans \| Minimum
Debt Instrument [Line Items]
Interest rate	4.03%	4.03%
Joint Ventures \| Commercial Mortgage Loans \| Maximum
Debt Instrument [Line Items]
Interest rate	4.96%	4.96%
Joint Ventures \| Commercial Mortgage Loans \| LIBOR
Debt Instrument [Line Items]
Mortgage carrying value	$ 16,029,000	$ 16,125,000
Mortgage principal	$ 16,325,000	16,125,000
Variable interest rate	2.15%
Virginia \| Commercial Mortgage Loans
Debt Instrument [Line Items]
Mortgage carrying value	$ 82,940,000	95,827,000
Mortgage principal	$ 84,702,000	$ 97,667,000
Virginia \| Commercial Mortgage Loans \| Minimum
Debt Instrument [Line Items]
Interest rate	2.34%	2.75%
Virginia \| Commercial Mortgage Loans \| Maximum
Debt Instrument [Line Items]
Interest rate	4.55%	4.96%
Texas \| Commercial Mortgage Loans
Debt Instrument [Line Items]
Mortgage carrying value	$ 31,667,000	$ 32,189,000
Mortgage principal	$ 33,167,000	$ 33,735,000
Interest rate	3.28%	3.28%
Utah \| Commercial Mortgage Loans
Debt Instrument [Line Items]
Mortgage carrying value	$ 7,077,000	$ 7,279,000
Mortgage principal	$ 7,096,000	$ 7,201,000
Interest rate	3.69%	3.69%
Utah \| Commercial Mortgage Loans \| LIBOR
Debt Instrument [Line Items]
Mortgage carrying value	$ 9,706,000	$ 9,703,000
Mortgage principal	$ 9,706,000	$ 9,706,000
Variable interest rate	3.50%	3.50%
Minnesota \| Commercial Mortgage Loans
Debt Instrument [Line Items]
Mortgage carrying value	$ 13,243,000	$ 13,438,000
Mortgage principal	$ 13,276,000	$ 13,473,000
Interest rate	3.69%	3.69%
Tennessee \| Commercial Mortgage Loans
Debt Instrument [Line Items]
Mortgage carrying value		$ 12,328,000
Mortgage principal		$ 12,350,000
Interest rate		4.01%
Tennessee \| Commercial Mortgage Loans \| LIBOR
Debt Instrument [Line Items]
Variable interest rate		2.75%
Wisconsin \| Commercial Mortgage Loans
Debt Instrument [Line Items]
Mortgage carrying value	$ 7,777,000	$ 7,892,000
Mortgage principal	$ 7,797,000	$ 7,913,000
Interest rate	3.69%	3.69%

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

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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/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)(1)
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-Publisher FASB
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-SubTopic 210
-Section S99
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-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
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Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28551-108399

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
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-SubTopic 30
-Section 55
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-URI http://asc.fasb.org/extlink&oid=114775985&loc=d3e28878-108400

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- Definition

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
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-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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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.

+ References

No definition available.

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