LEASES (UNITED DOMINION REALTY, L.P.) - Lessee Expenses (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Lessee operating leases
Contractual ground lease expense	$ 100	$ 100	$ 200	$ 200
Variable ground lease expense	0	100	100	200
Operating lease right-of-use asset amortization			1,600	400
Operating lease liabilities amortization			1,500	200
Ground Leases
Lessee operating leases
Contractual ground lease expense	3,216	2,139	6,386	4,278
Variable ground lease expense	44	143	87	282
United Dominion Realty L.P.
Lessee operating leases
Contractual ground lease expense	100	100	200	200
Total lease expense	3,298	2,282	6,547	4,560
Operating lease right-of-use asset amortization			1,700
Operating lease liabilities amortization			1,500
United Dominion Realty L.P. | Ground Leases
Lessee operating leases
Contractual ground lease expense	3,216	2,139	6,386	4,278
Variable ground lease expense	44	143	87	282
Total lease expense	3,260	$ 2,282	6,473	$ 4,560
United Dominion Realty L.P. | Equipment Leases
Lessee operating leases
Total lease expense	$ 38		$ 74