LEASES (UNITED DOMINION REALTY, L.P.) - Lessee Expenses (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Lessee operating leases
Contractual ground lease expense	$ 100	$ 100
Variable ground lease expense	100	200
Operating lease right-of-use asset amortization	800	200
Operating lease liabilities amortization	700	100
Ground Leases
Lessee operating leases
Contractual ground lease expense	3,170	2,159
Variable ground lease expense	43	139
United Dominion Realty L.P.
Lessee operating leases
Contractual ground lease expense	100	100
Total lease expense	3,249	2,279
Operating lease right-of-use asset amortization	900
Operating lease liabilities amortization	900
United Dominion Realty L.P. | Ground Leases
Lessee operating leases
Contractual ground lease expense	3,170	2,140
Variable ground lease expense	43	139
Total lease expense	3,213	$ 2,279
United Dominion Realty L.P. | Equipment Leases
Lessee operating leases
Total lease expense	$ 36