SIGNIFICANT ACCOUNTING POLICIES (UNITED DOMINION REALTY, L.P.) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Accounting policies
Operating lease right-of-use assets	$ 203,410		$ 204,225
Operating lease liabilities	197,829		198,558
Development costs excluding direct costs and capitalized interest	6,900	$ 3,300
Interest capitalized during period	1,400	1,100
United Dominion Realty L.P.
Accounting policies
Operating lease right-of-use assets	204,723		205,668
Operating lease liabilities	199,149		$ 200,001
Development costs excluding direct costs and capitalized interest	400
Unrecognized Tax Benefits	0
United Dominion Realty L.P. | Maximum
Accounting policies
Development costs excluding direct costs and capitalized interest		100
Interest capitalized during period	$ 100	$ 100