ACQUISITIONS AND DISPOSITIONS - Disposals (Details)							3 Months Ended		6 Months Ended
	Jun. 23, 2017 USD ($) apartment	Jun. 20, 2017 USD ($) ft²	Jun. 08, 2017 USD ($) ft²	May 30, 2017 USD ($) apartment	Mar. 28, 2017 USD ($) ft²	Feb. 02, 2016 USD ($) room	Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($)	Dec. 31, 2017 USD ($)	Jun. 30, 2017 USD ($) agreement business	Jun. 30, 2016 USD ($) business	Dec. 31, 2016 USD ($)
Disposals
Number of business acquisitions | business										0	0
Disposed Property Information
Sales price										$ 642,886,000	$ 42,782,000
Gain on sale of real estate							$ 116,283,000	$ 0		304,017,000	24,739,000
Assets
Total assets							125,138,000			125,138,000		$ 0
Liabilities
Total liabilities							52,886,000			52,886,000		$ 0
Additional Information
Impairment of real estate							13,100,000	$ 0		13,100,000	$ 0
Disposal Group, Disposed of by Sale, Not Discontinued Operations
Assets
Investments in real estate, net							319,078,000			319,078,000
Deferred rent receivable and charges, net							22,089,000			22,089,000
Other intangible assets, net							129,000			129,000
Other assets							38,000			38,000
Total assets							341,334,000			341,334,000
Liabilities
Debt, net							64,777,000			64,777,000
Intangible liabilities, net							1,800,000			1,800,000
Total liabilities							66,577,000			66,577,000
Disposal Group, Held-for-sale, Not Discontinued Operations
Assets
Investments in real estate, net							118,221,000			118,221,000
Cash and cash equivalents							2,904,000			2,904,000
Restricted cash							51,000			51,000
Accounts receivable, net							251,000			251,000
Deferred rent receivable and charges, net							1,865,000			1,865,000
Other intangible assets, net							1,124,000			1,124,000
Other assets							722,000			722,000
Total assets							125,138,000			125,138,000
Liabilities
Debt, net							50,230,000			50,230,000
Accounts payable and accrued expenses							1,402,000			1,402,000
Due to related parties							195,000			195,000
Other liabilities							1,059,000			1,059,000
Total liabilities							52,886,000			52,886,000
Additional Information
Investments in real estate, gross							136,153,000			136,153,000
Investments in real estate, accumulated depreciation							17,932,000			17,932,000
Deferred loan costs							524,000			524,000
Deferred loan costs, accumulated amortization							186,000			186,000
211 Main Street, San Francisco | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Disposals
Ownership sold, percentage					100.00%
Sale transaction costs					$ 2,943,000
Mortgage prepayment penalty					$ 1,508,000
Disposed Property Information
Square feet | ft²					417,266
Sales price					$ 292,882,000
Gain on sale of real estate					187,734,000
Additional Information
Premium on assumed mortgage							665,000			$ 665,000
Payment of mortgages payable					$ 25,331,000
3636 McKinney Avenue and 3839 McKinney Avenue, Dallas, Texas | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Disposals
Ownership sold, percentage				100.00%
Sale transaction costs				$ 2,258,000
Mortgage prepayment penalty				1,901,000
Additional Information
Payment of mortgages payable				$ 15,448,000
3636 McKinney Avenue, Dallas, Texas | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Disposed Property Information
Number of units | apartment				103
Sales price				$ 20,000,000
Gain on sale of real estate				$ 5,488,000
3839 McKinney Avenue, Dallas, Texas | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Disposed Property Information
Number of units | apartment				75
Sales price				$ 14,100,000
Gain on sale of real estate				$ 4,224,000
200 S College Street, Charlotte, North Carolina | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Disposals
Ownership sold, percentage			100.00%
Sale transaction costs			$ 833,000
Disposed Property Information
Square feet | ft²			567,865
Sales price			$ 148,500,000
Gain on sale of real estate			$ 45,906,000
980 9th Street and 1010 8th Street, Sacramento, California | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Disposals
Ownership sold, percentage		100.00%
Sale transaction costs		$ 952,000
Disposed Property Information
Square feet | ft²		485,926
Sales price		$ 120,500,000
Gain on sale of real estate		$ 34,829,000
4649 Cole Avenue, Dallas, Texas | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Disposals
Ownership sold, percentage	100.00%
Sale transaction costs	$ 3,311,000
Mortgage prepayment penalty	$ 2,812,000
Disposed Property Information
Number of units | apartment	334
Sales price	$ 64,000,000
Gain on sale of real estate	25,836,000
Additional Information
Payment of mortgages payable	$ 23,333,000
Courtyard Oakland located in Oakland California | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Disposals
Ownership sold, percentage						100.00%
Disposed Property Information
Number of rooms | room						162
Sales price						$ 43,800,000
Gain on sale of real estate						$ 24,739,000
7083 Hollywood Boulevard, 4200 Scotland Street, 47 E 34th Street
Additional Information
Number of purchase and sales agreements entered into | agreement										3
47 E 34th Street | Disposal Group, Held-for-sale, Not Discontinued Operations
Additional Information
Other intangible assets, gross							4,273,000			$ 4,273,000
Other intangible assets, accumulated amortization							3,149,000			3,149,000
7083 Hollywood Boulevard | Disposal Group, Held-for-sale, Not Discontinued Operations
Additional Information
Debt, gross							21,700,000			21,700,000
4200 Scotland Street | Disposal Group, Held-for-sale, Not Discontinued Operations
Additional Information
Debt, gross							28,868,000			$ 28,868,000
370 L'Enfant Promenade, Washington D.C.
Additional Information
Impairment of real estate							$ 13,100,000
Scenario, Forecast
Additional Information
Payment of mortgages payable									$ 50,568,000
Scenario, Forecast | 7083 Hollywood Boulevard, 4200 Scotland Street, 47 E 34th Street
Disposed Property Information
Sales price									$ 186,325,000