BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Reclassifications (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Consolidated Statements of Operations
Asset management and other fees to related parties	$ 9,793	$ 13,121	$ 18,959
Consolidated Statements of Cash Flows
Depreciation and amortization	21,085	26,608	52,230
Straight-line rent, below-market ground lease and amortization of intangible assets		0	0
Deferred rent and amortization of intangible assets, liabilities and lease inducements		0	0
Other assets	1,233	1,019	(4,077)
Payment of unsecured revolving lines of credit, revolving credit facilities, mortgages payable, term notes and principal on SBA 7(a) loan-backed notes	(57,584)	(192,987)	(186,231)
Payment of mortgages payable		0	0
Proceeds from SBA 7(a) loan-backed notes		0	0
Payment of principal on SBA 7(a) loan-backed notes		0	0
Payment of deferred costs	(983)	(423)	(4,469)
Payment of deferred loan costs		0	0
Payment of common dividends	(4,431)	(13,141)	(21,895)
Retirement of fractional shares of Common Stock		0	0
Additions to deferred loan costs included in accounts payable and accrued expenses		0	0
Accrued deferred costs	125	35	206
Preferred stock offering costs offset against redeemable preferred stock	583	350	229
Preferred stock offering costs offset against redeemable preferred stock in permanent equity		0	0
Corporate, Non-Segment
Consolidated Statements of Operations
Expense reimbursements to related parties	2,243	2,800	3,047
Operating Segments
Consolidated Statements of Operations
Expense reimbursements to related parties	$ 3,491	2,382	2,445
As previously reported
Consolidated Statements of Operations
Asset management and other fees to related parties		18,303	24,451
Consolidated Statements of Cash Flows
Depreciation and amortization		27,374	53,228
Straight-line rent, below-market ground lease and amortization of intangible assets		0	(18)
Deferred rent and amortization of intangible assets, liabilities and lease inducements		(2,727)	(3,636)
Other assets		2,980	(1,421)
Payment of unsecured revolving lines of credit, revolving credit facilities, mortgages payable, term notes and principal on SBA 7(a) loan-backed notes		(135,500)	(220,000)
Payment of mortgages payable		(46,000)	0
Proceeds from SBA 7(a) loan-backed notes		0	38,200
Payment of principal on SBA 7(a) loan-backed notes		(11,487)	(4,431)
Payment of deferred costs		(389)	(235)
Payment of deferred loan costs		(34)	(4,234)
Payment of common dividends		(13,140)	(21,895)
Retirement of fractional shares of Common Stock		(1)	0
Additions to deferred loan costs included in accounts payable and accrued expenses		0	32
Accrued deferred costs		35	174
Preferred stock offering costs offset against redeemable preferred stock		347	229
Preferred stock offering costs offset against redeemable preferred stock in permanent equity		3	0
As previously reported | Corporate, Non-Segment
Consolidated Statements of Operations
Expense reimbursements to related parties		0	0
As previously reported | Operating Segments
Consolidated Statements of Operations
Expense reimbursements to related parties		0	0
Reclassification
Consolidated Statements of Operations
Asset management and other fees to related parties		(5,182)	(5,492)
Consolidated Statements of Cash Flows
Depreciation and amortization		(766)	(998)
Straight-line rent, below-market ground lease and amortization of intangible assets		0	18
Deferred rent and amortization of intangible assets, liabilities and lease inducements		2,727	3,636
Other assets		(1,961)	(2,656)
Payment of unsecured revolving lines of credit, revolving credit facilities, mortgages payable, term notes and principal on SBA 7(a) loan-backed notes		(57,487)	33,769
Payment of mortgages payable		46,000	0
Proceeds from SBA 7(a) loan-backed notes		0	(38,200)
Payment of principal on SBA 7(a) loan-backed notes		11,487	4,431
Payment of deferred costs		(34)	(4,234)
Payment of deferred loan costs		34	4,234
Payment of common dividends		(1)	0
Retirement of fractional shares of Common Stock		1	0
Additions to deferred loan costs included in accounts payable and accrued expenses		0	(32)
Accrued deferred costs		0	32
Preferred stock offering costs offset against redeemable preferred stock		3	0
Preferred stock offering costs offset against redeemable preferred stock in permanent equity		(3)	0
Reclassification | Corporate, Non-Segment
Consolidated Statements of Operations
Expense reimbursements to related parties		2,800	3,047
Reclassification | Operating Segments
Consolidated Statements of Operations
Expense reimbursements to related parties		$ 2,382	$ 2,445