ACQUISITIONS AND DISPOSITIONS - Disposals (Details) $ in Thousands									3 Months Ended		9 Months Ended
	Sep. 26, 2017 USD ($) apartment	Sep. 21, 2017 USD ($) ft²	Aug. 31, 2017 USD ($) ft²	Jun. 23, 2017 USD ($) apartment	Jun. 20, 2017 USD ($) ft²	Jun. 08, 2017 USD ($) ft²	May 30, 2017 USD ($) apartment	Mar. 28, 2017 USD ($) ft²	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)
Disposed Property Information
Sales Price											$ 0	$ 851,629
Gain on sale of real estate									$ 0	$ 74,715	$ 0	$ 378,732
Disposal Group, Disposed of by Sale, Not Discontinued Operations
Disposals
Ownership sold, percentage												100.00%
Assets
Investments in real estate, net										469,816		$ 469,816
Deferred rent receivable and charges, net										29,954		29,954
Other intangible assets, net										11,283		11,283
Other assets										38		38
Total assets										511,091		511,091
Liabilities
Debt, net										86,477		86,477
Other liabilities										14,029		14,029
Intangible liabilities, net										1,800		1,800
Total liabilities										102,306		102,306
Additional Information
Premium on assumed mortgage										$ 665		$ 665
Disposal Group, Disposed of by Sale, Not Discontinued Operations | 211 Main Street, San Francisco, CA
Disposed Property Information
Square Feet | ft²								417,266
Sales Price								$ 292,882
Transaction Costs								2,943
Gain on sale of real estate								187,734
Mortgage prepayment penalty								$ 1,508
Disposal Group, Disposed of by Sale, Not Discontinued Operations | 3636 McKinney Avenue, Dallas, TX
Disposed Property Information
Number of units | apartment							103
Sales Price							$ 20,000
Transaction Costs							1,320
Gain on sale of real estate							5,488
Mortgage prepayment penalty							$ 1,143
Disposal Group, Disposed of by Sale, Not Discontinued Operations | 3839 McKinney Avenue, Dallas, TX
Disposed Property Information
Number of units | apartment							75
Sales Price							$ 14,100
Transaction Costs							938
Gain on sale of real estate							4,224
Mortgage prepayment penalty							$ 758
Disposal Group, Disposed of by Sale, Not Discontinued Operations | 200 S College Street, Charlotte, NC
Disposed Property Information
Square Feet | ft²						567,865
Sales Price						$ 148,500
Transaction Costs						833
Gain on sale of real estate						$ 45,906
Disposal Group, Disposed of by Sale, Not Discontinued Operations | 980 9th Street and 1010 8th Street, Sacramento, CA
Disposed Property Information
Square Feet | ft²					485,926
Sales Price					$ 120,500
Transaction Costs					1,119
Gain on sale of real estate					$ 34,559
Disposal Group, Disposed of by Sale, Not Discontinued Operations | 4649 Cole Avenue, Dallas, TX
Disposed Property Information
Number of units | apartment				334
Sales Price				$ 64,000
Transaction Costs				3,311
Gain on sale of real estate				25,836
Mortgage prepayment penalty				$ 2,812
Disposal Group, Disposed of by Sale, Not Discontinued Operations | 800 N Capitol Street, Washington, D.C.
Disposed Property Information
Square Feet | ft²			311,593
Sales Price			$ 119,750
Transaction Costs			2,388
Gain on sale of real estate			$ 34,456
Disposal Group, Disposed of by Sale, Not Discontinued Operations | 7083 Hollywood Boulevard, Los Angeles, CA (4)
Disposed Property Information
Square Feet | ft²		82,193
Sales Price		$ 42,300
Transaction Costs		584
Gain on sale of real estate		$ 23,670
Disposal Group, Disposed of by Sale, Not Discontinued Operations | 47 E 34th Street, New York, NY
Disposed Property Information
Number of units | apartment	110
Sales Price	$ 80,000
Transaction Costs	3,157
Gain on sale of real estate	$ 16,556