INVESTMENT IN UNCONSOLIDATED JOINT VENTURES - Additional Information (Details)		1 Months Ended	3 Months Ended		6 Months Ended
		Apr. 30, 2012	Jun. 30, 2019 USD ($) property	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) property	Jun. 30, 2018 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Mar. 22, 2013
Schedule of Equity Method Investments [Line Items]
Investments in and advances to unconsolidated joint ventures	[1]		$ 57,751,000		$ 57,751,000			$ 40,354,000
Distributions from operations of investment in unconsolidated joint ventures					3,067,000	$ 0
Income (expenses) from investment			(3,571,000)	$ (2,801,000)	(7,434,000)	(6,373,000)
Grace Lake JV, LLC
Schedule of Equity Method Investments [Line Items]
Investments in and advances to unconsolidated joint ventures			$ 3,282,000		$ 3,282,000			5,316,000
Percentage of equity kicker received with right to convert upon capital event		25.00%
Preferred return used to determine distribution of excess cash flow					8.25%
Percentage of distribution of all excess cash flows and all disposition proceeds upon any sale entitled after consideration of preferred return and return of equity remaining in the property to operating partner					25.00%
Percentage of investment of operating partner					81.00%
Distributions from operations of investment in unconsolidated joint ventures					$ 0	1,300,000
Grace Lake JV, LLC | LP Units
Schedule of Equity Method Investments [Line Items]
Ownership interest									19.00%
Grace Lake JV, LLC | Limited liability company
Schedule of Equity Method Investments [Line Items]
Ownership interest			19.00%		19.00%
24 Second Avenue Holdings LLC
Schedule of Equity Method Investments [Line Items]
Investments in and advances to unconsolidated joint ventures			$ 54,469,000		$ 54,469,000			35,038,000
Income (expenses) from investment			$ 900,000	(300,000)	1,500,000	(500,000)
Interest costs capitalized				$ 400,000	$ 100,000	$ 700,000
24 Second Avenue Holdings LLC | Apartment Building
Schedule of Equity Method Investments [Line Items]
Number of real estate properties | property			30		30
Number of real estate properties, under contract | property			1		1
Real estate properties, under contract			$ 4,300,000		$ 4,300,000
24 Second Avenue Holdings LLC | Apartment Building | Maximum
Schedule of Equity Method Investments [Line Items]
Real estate properties, under contract, deposit			15.00%		15.00%
24 Second Avenue Holdings LLC | Apartment Building | Real Estate Property Sold
Schedule of Equity Method Investments [Line Items]
Number of real estate properties, under contract | property			15		15
Real estate properties, under contract			$ 40,100,000		$ 40,100,000
24 Second Avenue Holdings LLC | Other
Schedule of Equity Method Investments [Line Items]
Number of real estate properties | property			1		1
24 Second Avenue Holdings LLC | Mezzanine Loan
Schedule of Equity Method Investments [Line Items]
Committed amount on credit agreement							$ 6,500,000
24 Second Avenue Holdings LLC | Co-venturer
Schedule of Equity Method Investments [Line Items]
Loans payable outstanding from unconsolidated joint venture								$ 46,700,000
24 Second Avenue Holdings LLC | Co-venturer | Construction Loan
Schedule of Equity Method Investments [Line Items]
Common equity interest							35,000,000.0
Preferred equity position							35,000,000.0
Loan refinance							50,400,000
Committed amount on credit agreement							$ 48,100,000
Remaining capital commitment to operating partner			$ 0		$ 0

[1] Includes amounts relating to consolidated variable interest entities. See Note 3.