LEASES (UNITED DOMINION REALTY, L.P.) - Lessee Expenses (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Lessee operating leases
Contractual ground lease expense	$ 100	$ 100	$ 300	$ 300
Variable ground lease expense		100	100	300
Operating lease right-of-use asset amortization			2,500	600
Operating lease liabilities amortization			2,200	300
Ground Leases
Lessee operating leases
Contractual ground lease expense	3,217	1,954	9,603	6,232
Variable ground lease expense	33	187	120	469
United Dominion Realty L.P.
Lessee operating leases
Contractual ground lease expense	100	100	300	300
Total lease expense	3,289	2,141	9,836	6,701
Operating lease right-of-use asset amortization			2,500
Operating lease liabilities amortization			2,200
United Dominion Realty L.P. | Ground Leases
Lessee operating leases
Contractual ground lease expense	3,217	1,954	9,603	6,232
Variable ground lease expense	33	187	120	469
Total lease expense	3,250	$ 2,141	9,723	$ 6,701
United Dominion Realty L.P. | Equipment Leases
Lessee operating leases
Total lease expense	$ 39		$ 113