MORTGAGES PAYABLE - Summary of Mortgages Payable (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Debt Instrument [Line Items]
Total mortgages payable, net of unamortized debt issuance costs	$ 1,866,853		$ 1,546,195
Mortgages | First Mortgage
Debt Instrument [Line Items]
Total mortgages payable	1,626,443		1,556,248
Unamortized debt issuance costs	(9,590)		(10,053)
Total mortgages payable, net of unamortized debt issuance costs	1,616,853		1,546,195
Mortgages | First Mortgage | Variable rate
Debt Instrument [Line Items]
Total mortgages payable	$ 169,151		169,500
Mortgages | First Mortgage | Variable rate | The Plaza at Cherry Hill
Debt Instrument [Line Items]
Interest rate	3.18%
Total mortgages payable	$ 28,930		28,930
Mortgages | First Mortgage | Variable rate | The Plaza at Cherry Hill | LIBOR
Debt Instrument [Line Items]
Interest rate spread on variable rate	160.00%	160.00%
Mortgages | First Mortgage | Variable rate | Westfield - One Lincoln Plaza
Debt Instrument [Line Items]
Interest rate	3.18%
Total mortgages payable	$ 4,730		4,730
Mortgages | First Mortgage | Variable rate | Westfield - One Lincoln Plaza | LIBOR
Debt Instrument [Line Items]
Interest rate spread on variable rate	160.00%	160.00%
Mortgages | First Mortgage | Variable rate | The Plaza at Woodbridge
Debt Instrument [Line Items]
Interest rate	3.18%
Total mortgages payable	$ 55,340		55,340
Mortgages | First Mortgage | Variable rate | The Plaza at Woodbridge | LIBOR
Debt Instrument [Line Items]
Interest rate spread on variable rate	160.00%	160.00%
Mortgages | First Mortgage | Variable rate | Hudson Commons
Debt Instrument [Line Items]
Interest rate	3.48%
Total mortgages payable	$ 28,862		29,000
Mortgages | First Mortgage | Variable rate | Hudson Commons | LIBOR
Debt Instrument [Line Items]
Interest rate spread on variable rate	190.00%
Mortgages | First Mortgage | Variable rate | Watchung, NJ
Debt Instrument [Line Items]
Interest rate	3.48%
Total mortgages payable	$ 26,871		27,000
Mortgages | First Mortgage | Variable rate | Watchung, NJ | LIBOR
Debt Instrument [Line Items]
Interest rate spread on variable rate	190.00%
Mortgages | First Mortgage | Variable rate | Bronx (1750-1780 Gun Hill Road), NY
Debt Instrument [Line Items]
Interest rate	3.48%
Total mortgages payable	$ 24,418		24,500
Mortgages | First Mortgage | Variable rate | Bronx (1750-1780 Gun Hill Road), NY | LIBOR
Debt Instrument [Line Items]
Interest rate spread on variable rate	190.00%
Mortgages | First Mortgage | Fixed rate
Debt Instrument [Line Items]
Total mortgages payable	$ 1,457,292		1,386,748
Mortgages | First Mortgage | Fixed rate | Montehiedra Town Center | Senior Loan
Debt Instrument [Line Items]
Interest rate	5.33%
Total mortgages payable	$ 82,876		83,202
Mortgages | First Mortgage | Fixed rate | Montehiedra Town Center | Junior Loan
Debt Instrument [Line Items]
Interest rate	3.00%
Total mortgages payable	$ 30,000		30,000
Mortgages | First Mortgage | Fixed rate | Bergen Town Center
Debt Instrument [Line Items]
Interest rate	3.56%
Total mortgages payable	$ 300,000		300,000
Mortgages | First Mortgage | Fixed rate | Shops at Bruckner
Debt Instrument [Line Items]
Interest rate	3.90%
Total mortgages payable	$ 10,823		10,978
Mortgages | First Mortgage | Fixed rate | Hudson Mall
Debt Instrument [Line Items]
Interest rate	5.07%
Total mortgages payable	$ 23,445		23,625
Effective interest rate	3.85%
Unamortized debt premium	$ 900		1,000
Mortgages | First Mortgage | Fixed rate | Yonkers Gateway Center
Debt Instrument [Line Items]
Interest rate	4.16%
Total mortgages payable	$ 29,717		30,122
Effective interest rate	3.70%
Unamortized debt premium	$ 500		600
Mortgages | First Mortgage | Fixed rate | Las Catalinas
Debt Instrument [Line Items]
Interest rate	4.43%
Total mortgages payable	$ 128,822		129,335
Mortgages | First Mortgage | Fixed rate | Brick, NJ
Debt Instrument [Line Items]
Interest rate	3.87%
Total mortgages payable	$ 50,000		50,000
Mortgages | First Mortgage | Fixed rate | North Plainfield
Debt Instrument [Line Items]
Interest rate	3.99%
Total mortgages payable	$ 25,100		25,100
Mortgages | First Mortgage | Fixed rate | Middletown, NJ
Debt Instrument [Line Items]
Interest rate	3.78%
Total mortgages payable	$ 31,400		31,400
Mortgages | First Mortgage | Fixed rate | Rockaway
Debt Instrument [Line Items]
Interest rate	3.78%
Total mortgages payable	$ 27,800		27,800
Mortgages | First Mortgage | Fixed rate | East Hanover (200 - 240 Route 10 West), NJ
Debt Instrument [Line Items]
Interest rate	4.03%
Total mortgages payable	$ 63,000		63,000
Mortgages | First Mortgage | Fixed rate | North Bergen (Tonnelle Avenue), NJ
Debt Instrument [Line Items]
Interest rate	4.18%
Total mortgages payable	$ 100,000		100,000
Mortgages | First Mortgage | Fixed rate | Manchester Plaza
Debt Instrument [Line Items]
Interest rate	4.32%
Total mortgages payable	$ 12,500		12,500
Mortgages | First Mortgage | Fixed rate | Millburn
Debt Instrument [Line Items]
Interest rate	3.97%
Total mortgages payable	$ 23,694		23,798
Mortgages | First Mortgage | Fixed rate | Totowa, NJ
Debt Instrument [Line Items]
Interest rate	4.33%
Total mortgages payable	$ 50,800		50,800
Mortgages | First Mortgage | Fixed rate | Woodbridge Commons
Debt Instrument [Line Items]
Interest rate	4.36%
Total mortgages payable	$ 22,100		22,100
Mortgages | First Mortgage | Fixed rate | East Brunswick, NJ
Debt Instrument [Line Items]
Interest rate	4.38%
Total mortgages payable	$ 63,000		63,000
Mortgages | First Mortgage | Fixed rate | East Rutherford, NJ
Debt Instrument [Line Items]
Interest rate	4.49%
Total mortgages payable	$ 23,000		23,000
Mortgages | First Mortgage | Fixed rate | Brooklyn (Kingswood Center)
Debt Instrument [Line Items]
Interest rate	5.07%
Total mortgages payable	$ 72,356		0
Effective interest rate	3.44%
Unamortized debt premium	$ 6,900
Mortgages | First Mortgage | Fixed rate | Hackensack, NJ
Debt Instrument [Line Items]
Interest rate	4.36%
Total mortgages payable	$ 66,400		66,400
Mortgages | First Mortgage | Fixed rate | Marlton, NJ
Debt Instrument [Line Items]
Interest rate	3.86%
Total mortgages payable	$ 37,400		37,400
Mortgages | First Mortgage | Fixed rate | East Hanover Warehouses
Debt Instrument [Line Items]
Interest rate	4.09%
Total mortgages payable	$ 40,700		40,700
Mortgages | First Mortgage | Fixed rate | Union (2445 Springfield Avenue), NJ
Debt Instrument [Line Items]
Interest rate	4.01%
Total mortgages payable	$ 45,600		45,600
Mortgages | First Mortgage | Fixed rate | Freeport (437 East Sunrise Highway), NY
Debt Instrument [Line Items]
Interest rate	4.07%
Total mortgages payable	$ 43,100		43,100
Mortgages | First Mortgage | Fixed rate | Garfield, NJ
Debt Instrument [Line Items]
Interest rate	4.14%
Total mortgages payable	$ 40,300		40,300
Mortgages | First Mortgage | Fixed rate | Mount Kisco (Target)
Debt Instrument [Line Items]
Interest rate	6.40%
Total mortgages payable	$ 13,359		13,488
Unamortized debt discount			(900)
Effective interest rate	7.30%
Revolving Credit Facility | Line of Credit
Debt Instrument [Line Items]
Interest rate	2.00%
Total mortgages payable	$ 250,000		0
Total mortgages payable, net of unamortized debt issuance costs	$ 250,000		$ 0
Revolving Credit Facility | Line of Credit | LIBOR
Debt Instrument [Line Items]
Interest rate spread on variable rate	1.05%