FAIR VALUE OF DERIVATIVES AND FINANCIAL INSTRUMENTS (UNITED DOMINION REALTY, L.P.) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Debt instruments - fair value
Transfer between the levels	$ 0
Fair Value, Measurements, Recurring | Carrying Amount
Debt instruments - fair value
Total liabilities	4,913,746	$ 4,731,595
Fair Value, Measurements, Recurring | Fair Value
Debt instruments - fair value
Total liabilities	4,907,068	4,853,337
Level 2 | Fair Value, Measurements, Recurring | Fair Value
Debt instruments - fair value
Total liabilities	3,075	142
Level 3 | Fair Value, Measurements, Recurring | Fair Value
Debt instruments - fair value
Total liabilities	4,903,993	4,853,195
United Dominion Realty L.P. | Fair Value, Measurements, Recurring | Carrying Amount
Debt instruments - fair value
Total liabilities	99,500	99,500
United Dominion Realty L.P. | Fair Value, Measurements, Recurring | Fair Value
Debt instruments - fair value
Total liabilities	100,663	98,976
United Dominion Realty L.P. | Mortgages Note Payable | Fair Value, Measurements, Recurring | Carrying Amount
Debt instruments - fair value
Fair value		72,500
United Dominion Realty L.P. | Mortgages Note Payable | Fair Value, Measurements, Recurring | Fair Value
Debt instruments - fair value
Fair value		71,976
United Dominion Realty L.P. | Level 3 | Fair Value, Measurements, Recurring | Fair Value
Debt instruments - fair value
Total liabilities	100,663	98,976
United Dominion Realty L.P. | Level 3 | Mortgages Note Payable | Fair Value, Measurements, Recurring | Fair Value
Debt instruments - fair value
Fair value		71,976
Fixed Rate Debt | United Dominion Realty L.P. | Mortgages Note Payable | Fair Value, Measurements, Recurring | Carrying Amount
Debt instruments - fair value
Fair value	72,500
Fixed Rate Debt | United Dominion Realty L.P. | Mortgages Note Payable | Fair Value, Measurements, Recurring | Fair Value
Debt instruments - fair value
Fair value	73,663
Fixed Rate Debt | United Dominion Realty L.P. | Level 3 | Mortgages Note Payable | Fair Value, Measurements, Recurring | Fair Value
Debt instruments - fair value
Fair value	73,663
Variable Rate Debt | United Dominion Realty L.P. | Tax-exempt secured notes payable | Fair Value, Measurements, Recurring | Carrying Amount
Debt instruments - fair value
Fair value	27,000	27,000
Variable Rate Debt | United Dominion Realty L.P. | Tax-exempt secured notes payable | Fair Value, Measurements, Recurring | Fair Value
Debt instruments - fair value
Fair value	27,000	27,000
Variable Rate Debt | United Dominion Realty L.P. | Level 3 | Tax-exempt secured notes payable | Fair Value, Measurements, Recurring | Fair Value
Debt instruments - fair value
Fair value	$ 27,000	$ 27,000