SIGNIFICANT ACCOUNTING POLICIES (UNITED DOMINION REALTY, L.P.) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2019
Accounting policies
Operating lease right-of-use assets	$ 204,225
Operating lease liabilities	198,558
Development costs excluding direct costs and capitalized interest	8,400	$ 7,500	$ 8,800
Interest capitalized during period	5,100	10,600	18,600
Advertising expense	$ 6,500	6,700	6,200
Minimum percentage of carrying value of real estate portfolio	10.00%
Minimum | Buildings
Accounting policies
Estimated useful lives	30 years
Minimum | Building improvements
Accounting policies
Estimated useful lives	10 years
Minimum | Furniture, fixtures, equipment, and other assets
Accounting policies
Estimated useful lives	3 years
Maximum | Buildings
Accounting policies
Estimated useful lives	55 years
Maximum | Building improvements
Accounting policies
Estimated useful lives	35 years
Maximum | Furniture, fixtures, equipment, and other assets
Accounting policies
Estimated useful lives	10 years
United Dominion Realty L.P.
Accounting policies
Operating lease right-of-use assets	$ 205,668
Operating lease liabilities	200,001
Development costs excluding direct costs and capitalized interest	800	100	500
Interest capitalized during period	200
Unrecognized Tax Benefits	0
Advertising expense	$ 1,900	1,900	2,100
Minimum percentage of carrying value of real estate portfolio	10.00%
United Dominion Realty L.P. | Minimum | Buildings
Accounting policies
Estimated useful lives	30 years
United Dominion Realty L.P. | Minimum | Building improvements
Accounting policies
Estimated useful lives	10 years
United Dominion Realty L.P. | Minimum | Furniture, fixtures, equipment, and other assets
Accounting policies
Estimated useful lives	3 years
United Dominion Realty L.P. | Maximum
Accounting policies
Interest capitalized during period		100	$ 100
United Dominion Realty L.P. | Maximum | Buildings
Accounting policies
Estimated useful lives	55 years
United Dominion Realty L.P. | Maximum | Building improvements
Accounting policies
Estimated useful lives	35 years
United Dominion Realty L.P. | Maximum | Furniture, fixtures, equipment, and other assets
Accounting policies
Estimated useful lives	10 years
ASU 2016-02 | Adjustment
Accounting policies
Operating lease right-of-use assets				$ 94,300
Operating lease liabilities				88,300
Prepaid rent and intangible assets				6,000
ASU 2016-02 | Adjustment | United Dominion Realty L.P.
Accounting policies
Operating lease right-of-use assets				94,200
Operating lease liabilities				$ 88,200
Prepaid rent and intangible assets		$ 6,000