INVESTMENT IN UNCONSOLIDATED JOINT VENTURES - Summarized Financial Information (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Balance Sheet Related Disclosures [Abstract]
Real estate assets, net of accumulated depreciation and amortization	$ 768,414,000		$ 768,414,000		$ 759,479,000
Total assets	1,065,855,000		1,065,855,000		1,041,242,000
Other liabilities	19,472,000		19,472,000		19,801,000
Total liabilities, mezzanine equity and equity	1,065,855,000		1,065,855,000		1,041,242,000
Income Statement [Abstract]
Revenues	23,521,000	$ 21,689,000	48,121,000	$ 43,600,000
Real estate taxes and insurance	3,351,000	3,301,000	6,779,000	6,279,000
Depreciation and amortization	8,964,000	8,357,000	17,947,000	16,037,000
Interest expense	5,985,000	7,249,000	12,781,000	14,417,000
Total expenses	31,437,000	32,193,000	47,872,000	62,530,000
Net income (loss) attributable to common stockholders	3,668,000	(6,249,000)	(14,304,000)	10,532,000
Equity in income (loss) of unconsolidated entities	665,000	(215,000)	993,000	7,096,000
110 William Joint Venture
Balance Sheet Related Disclosures [Abstract]
Real estate assets, net of accumulated depreciation and amortization	247,301,000		247,301,000		242,430,000
Other assets	39,971,000		39,971,000		35,747,000
Total assets	287,272,000		287,272,000		278,177,000
Notes payable, net	308,441,000		308,441,000		292,221,000
Other liabilities	7,992,000		7,992,000		10,664,000
Partners’ deficit	(29,161,000)		(29,161,000)		(24,708,000)
Total liabilities, mezzanine equity and equity	287,272,000		287,272,000		278,177,000
Income Statement [Abstract]
Revenues	8,617,000	9,442,000	16,599,000	17,701,000
Real estate taxes and insurance	1,822,000	1,725,000	3,645,000	3,430,000
Depreciation and amortization	2,939,000	2,839,000	5,582,000	5,503,000
Interest expense	4,042,000	4,124,000	7,968,000	8,732,000
Total expenses	10,399,000	10,968,000	21,093,000	22,117,000
Total other income	16,000	39,000	38,000	71,000
Net income (loss) attributable to common stockholders	(1,766,000)	(1,487,000)	(4,456,000)	(4,345,000)
Company’s share of net loss	(1,060,000)	(892,000)	(2,674,000)	(2,607,000)
Loss from equity method investments		0		300,000
110 William Joint Venture | Operating, maintenance, and management costs
Income Statement [Abstract]
Expenses	1,596,000	2,280,000	3,898,000	4,452,000
353 Sacramento Joint Venture
Balance Sheet Related Disclosures [Abstract]
Real estate assets, net of accumulated depreciation and amortization	184,980,000		184,980,000		180,592,000
Other assets	18,850,000		18,850,000		21,822,000
Total assets	203,830,000		203,830,000		202,414,000
Notes payable, net	115,427,000		115,427,000		115,280,000
Other liabilities	10,792,000		10,792,000		11,193,000
Partners’ deficit	77,611,000		77,611,000		75,941,000
Total liabilities, mezzanine equity and equity	203,830,000		203,830,000		$ 202,414,000
Income Statement [Abstract]
Revenues	5,364,000	4,187,000	10,251,000	8,345,000
Real estate taxes and insurance	728,000	694,000	1,481,000	1,395,000
Depreciation and amortization	1,639,000	1,563,000	3,241,000	3,131,000
Interest expense	1,021,000	1,447,000	2,342,000	2,866,000
Total expenses	4,224,000	4,643,000	8,581,000	9,161,000
Net income (loss) attributable to common stockholders	1,140,000	(456,000)	1,670,000	(816,000)
Equity in income (loss) of unconsolidated entities	665,000	(215,000)	993,000	(379,000)
353 Sacramento Joint Venture | Operating, maintenance, and management costs
Income Statement [Abstract]
Expenses	$ 836,000	$ 939,000	$ 1,517,000	$ 1,769,000