CONSOLIDATION AND BASIS OF PRESENTATION - GP Units (UNITED DOMINION REALTY, L.P.) (Details)	3 Months Ended
Sep. 30, 2018 community item shares	Dec. 31, 2017 shares
Basis of presentation
Number of real estate properties \| community	127
Number of apartments owned (in apartments homes) \| item	40,420
Operating Partnership units outstanding related to limited partner	183,636,543	183,350,924
United Dominion Reality L.P.
Basis of presentation
Rental revenues percent of General Partner's consolidated rental revenues	42.00%
General Partners Capital Account Units Owned Percentage	94.90%
Operating Partnership units outstanding related to limited partner	174,248,699
United Dominion Reality L.P.
Basis of presentation
Number of real estate properties \| community	52
Number of markets operating within (in markets) \| item	15
Number of apartments owned (in apartments homes) \| item	16,434
Operating Partnership outstanding units	183,636,543	183,350,924
OP units outstanding related to general partner	110,883	110,883
Operating Partnership units outstanding related to limited partner	183,525,660	183,240,041
UDR, Inc.
Basis of presentation
Operating Partnership units outstanding related to limited partner	174,137,816	174,126,805
Percentage of units outstanding in Heritage Operating Partnership	94.90%	95.00%
UDR, Inc. \| United Dominion Reality L.P.
Basis of presentation
General Partners Capital Account Units Owned Percentage	94.90%
Operating Partnership outstanding units		174,237,688
OP units outstanding related to general partner	174,248,699
Percentage of units outstanding in Heritage Operating Partnership		95.00%
Non-affiliated Partners \| United Dominion Reality L.P.
Basis of presentation
Operating Partnership outstanding units		9,113,236
Operating Partnership units outstanding related to limited partner	9,387,844
Percentage of units outstanding in Heritage Operating Partnership	5.10%	5.00%
Class A Limited Partner \| United Dominion Reality L.P.
Basis of presentation
Operating Partnership units outstanding related to limited partner	1,873,332	1,873,332
Class A Limited Partner \| UDR, Inc.
Basis of presentation
Operating Partnership units outstanding related to limited partner	121,661	121,661
Limited Partner
Basis of presentation
Operating Partnership units outstanding related to limited partner	7,636,173	7,361,565
Limited Partner \| UDR, Inc.
Basis of presentation
Operating Partnership units outstanding related to limited partner	174,016,155	174,005,144
General Partner \| UDR, Inc.
Basis of presentation
Operating Partnership units outstanding related to limited partner	110,883	110,883
Non-affiliated Partners \| United Dominion Reality L.P.
Basis of presentation
Operating Partnership units outstanding related to limited partner	9,387,844	9,113,236
Percentage of units outstanding in Heritage Operating Partnership	5.10%	5.00%
Non-affiliated Partners \| Class A Limited Partner
Basis of presentation
Operating Partnership units outstanding related to limited partner	1,751,671	1,751,671

[Line Items] for Consolidation and Basis of Presentation [Table]

No definition available.

Name:	udr_ConsolidationAndBasisOfPresentationLineItems
Namespace Prefix:	udr_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

General Partners Capital Account Units Owned Percentage.

+ References

No definition available.

+ Details

Name:	udr_GeneralPartnersCapitalAccountUnitsOwnedPercentage
Namespace Prefix:	udr_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Limited Partners Capital Account Units Outstanding Percentage.

+ References

No definition available.

+ Details

Name:	udr_LimitedPartnersCapitalAccountUnitsOutstandingPercentage
Namespace Prefix:	udr_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Number Of Apartment Homes Owned And Consolidated By Company

+ References

No definition available.

+ Details

Name:	udr_NumberOfApartmentHomesOwnedAndConsolidatedByCompany
Namespace Prefix:	udr_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of Markets Operating Within

+ References

No definition available.

+ Details

Name:	udr_NumberOfMarketsOperatingWithin
Namespace Prefix:	udr_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Rental Revenues, Percent of Parent Revenue

+ References

No definition available.

+ Details

Name:	udr_RentalRevenuesPercentOfParentRentalRevenue
Namespace Prefix:	udr_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of general partner units outstanding.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 5
-Subparagraph (SAB Topic 4.F)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187171-122770

+ Details

Name:	us-gaap_GeneralPartnersCapitalAccountUnitsOutstanding
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

The number of limited partner units outstanding.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 272
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6373374&loc=d3e70434-108055

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 5
-Subparagraph (SAB Topic 4.F)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187171-122770

+ Details

Name:	us-gaap_LimitedPartnersCapitalAccountUnitsOutstanding
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

The number of real estate properties owned as of the balance sheet date.

+ References

No definition available.

+ Details

Name:	us-gaap_NumberOfRealEstateProperties
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

The number of each class of partnership units outstanding at the balance sheet date. Units represent shares of ownership of the general, limited, and preferred partners.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-04.16(b))
-URI http://asc.fasb.org/extlink&oid=6488278&loc=d3e603758-122996

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-04.16(a))
-URI http://asc.fasb.org/extlink&oid=6488278&loc=d3e603758-122996

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 5
-Subparagraph (SAB TOPIC 4.F)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187171-122770

+ Details

Name:	us-gaap_PartnersCapitalAccountUnits
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	us-gaap_OwnershipAxis=udr_UnitedDominionRealityLPMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=udr_UnitedDominionRealityLPMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=udr_UdrIncMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=udr_NonAffiliatedPartnersMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LimitedPartnersCapitalAccountByClassAxis=udr_ClassLimitedPartnerMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PartnerTypeOfPartnersCapitalAccountAxis=us-gaap_LimitedPartnerMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PartnerTypeOfPartnersCapitalAccountAxis=us-gaap_GeneralPartnerMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PartnerTypeOfPartnersCapitalAccountAxis=udr_NonAffiliatedPartnersMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: