FAIR VALUE OF DERIVATIVES AND FINANCIAL INSTRUMENTS (UNITED DOMINION REALTY, L.P.) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Debt instruments - fair value
Transfer between the levels	$ 0
Fair Value, Measurements, Recurring | Carrying Amount
Debt instruments - fair value
Total liabilities	4,731,595	$ 3,566,018
Fair Value, Measurements, Recurring | Fair Value
Debt instruments - fair value
Total liabilities	4,853,337	3,532,104
Tax-exempt secured notes payable | Fair Value, Measurements, Recurring | Fair Value
Debt instruments - fair value
Fair value		94,700
Credit facilities | Fair Value, Measurements, Recurring | Fair Value
Debt instruments - fair value
Fair value	213,661
Level 2 | Fair Value, Measurements, Recurring | Fair Value
Debt instruments - fair value
Total liabilities	142	356
Level 3 | Fair Value, Measurements, Recurring | Fair Value
Debt instruments - fair value
Total liabilities	4,853,195	3,531,748
Level 3 | Credit facilities | Fair Value, Measurements, Recurring | Fair Value
Debt instruments - fair value
Fair value	213,661
United Dominion Realty L.P. | Fair Value, Measurements, Recurring | Carrying Amount
Debt instruments - fair value
Total liabilities	99,500	27,000
United Dominion Realty L.P. | Fair Value, Measurements, Recurring | Fair Value
Debt instruments - fair value
Total liabilities	98,976	27,000
United Dominion Realty L.P. | Level 3 | Fair Value, Measurements, Recurring
Debt instruments - fair value
Total liabilities	98,976
United Dominion Realty L.P. | Level 3 | Fair Value, Measurements, Recurring | Fair Value
Debt instruments - fair value
Total liabilities		27,000
Fixed Rate Debt | Mortgages Notes Payable | Fair Value, Measurements, Recurring | Fair Value
Debt instruments - fair value
Fair value	898,329	416,314
Fixed Rate Debt | Level 3 | Mortgages Notes Payable | Fair Value, Measurements, Recurring | Fair Value
Debt instruments - fair value
Fair value	898,329	416,314
Fixed Rate Debt | United Dominion Realty L.P. | Mortgages Notes Payable | Fair Value, Measurements, Recurring | Carrying Amount
Debt instruments - fair value
Fair value	72,500
Fixed Rate Debt | United Dominion Realty L.P. | Mortgages Notes Payable | Fair Value, Measurements, Recurring | Fair Value
Debt instruments - fair value
Fair value	71,976
Fixed Rate Debt | United Dominion Realty L.P. | Level 3 | Mortgages Notes Payable | Fair Value, Measurements, Recurring
Debt instruments - fair value
Fair value	71,976
Variable Rate Debt | Tax-exempt secured notes payable | Fair Value, Measurements, Recurring | Fair Value
Debt instruments - fair value
Fair value	27,000
Variable Rate Debt | Level 3 | Tax-exempt secured notes payable | Fair Value, Measurements, Recurring | Fair Value
Debt instruments - fair value
Fair value	27,000	94,700
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
Debt instruments - fair value
Fair value	$ 27,000	$ 27,000