UNCONSOLIDATED ENTITIES (UNITED DOMINION REALTY, L.P.) - Additional Information (Details) $ in Thousands	Sep. 30, 2020 USD ($) community item	Dec. 31, 2019 USD ($)
Unconsolidated entities
Number of real estate properties \| community	148
Number of apartment homes owned and consolidated \| item	47,488
Equity Method Investments \| $	$ 641,858	$ 585,490
United Dominion Realty L.P.
Unconsolidated entities
Number of real estate properties \| community	52
Number of apartment homes owned and consolidated \| item	16,434
Equity Method Investments \| $	$ 56,705	76,222
United Dominion Realty L.P. \| UDR Lighthouse DownREIT L.P.
Unconsolidated entities
Number of real estate properties \| community	12
Number of apartment homes owned and consolidated \| item	5,657
Equity Method Investments \| $	$ 56,700	$ 76,200

This item represents the carrying amount on the entity's balance sheet of its investment in common stock of an equity method investee. This is not an indicator of the fair value of the investment, rather it is the initial cost adjusted for the entity's share of earnings and losses of the investee, adjusted for any distributions (dividends) and other than temporary impairment (OTTI) losses recognized.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=109237563&loc=d3e33749-111570

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 25
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8813-108599

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.12)
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant