Debt (UNITED DOMINION REALTY, L.P.) (Details 2) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
2013	$ 244,111
2014	275,526
2015	511,065
2016	315,496
2017	620,664
Long-Term Debt, Maturities, Repayments of Principal in Year Six	350,000
Long-Term Debt, Maturities, Repayments of Principal in Year Seven	400,000
Long-Term Debt, Maturities, Repayment of Principal in Year Eight	96,409
Long-Term Debt, Maturities, Repayment of Principal in Year Nine	315,644
Long-Term Debt, Maturities, Repayments of Principal in Year Ten	427,600
Long-Term Debt, Maturities, Repayments of Principal after Year Ten	27,000
Long-term Debt, Gross	3,583,515
Debt Instrument, Unamortized Discount (Premium), Net	(12,720)
Total	1,376,945	$ 1,354,321
Secured Debt [Member]
Debt Instrument [Line Items]
2013	149,058
2014	275,526
2015	211,065
2016	315,496
2017	170,664
Long-Term Debt, Maturities, Repayments of Principal in Year Six	0
Long-Term Debt, Maturities, Repayments of Principal in Year Seven	0
Long-Term Debt, Maturities, Repayment of Principal in Year Eight	96,409
Long-Term Debt, Maturities, Repayment of Principal in Year Nine	0
Long-Term Debt, Maturities, Repayments of Principal in Year Ten	127,600
Long-Term Debt, Maturities, Repayments of Principal after Year Ten	27,000
Long-term Debt, Gross	1,372,818
Debt Instrument, Unamortized Discount (Premium), Net	4,127
Secured Debt [Member] \| Fixed Rate Debt
Debt Instrument [Line Items]
2013	149,058
2014	179,189
2015	73,096
2016	247,796
2017	170,664
Long-Term Debt, Maturities, Repayments of Principal in Year Six	0
Long-Term Debt, Maturities, Repayments of Principal in Year Seven	0
Long-Term Debt, Maturities, Repayment of Principal in Year Eight	0
Long-Term Debt, Maturities, Repayment of Principal in Year Nine	0
Long-Term Debt, Maturities, Repayments of Principal in Year Ten	127,600
Long-Term Debt, Maturities, Repayments of Principal after Year Ten	0
Long-term Debt, Gross	947,403
Debt Instrument, Unamortized Discount (Premium), Net	5,398
Secured Debt [Member] \| Variable Rate Debt
Debt Instrument [Line Items]
2013	0
2014	96,337
2015	137,969
2016	67,700
2017	0
Long-Term Debt, Maturities, Repayments of Principal in Year Six	0
Long-Term Debt, Maturities, Repayments of Principal in Year Seven	0
Long-Term Debt, Maturities, Repayment of Principal in Year Eight	96,409
Long-Term Debt, Maturities, Repayment of Principal in Year Nine	0
Long-Term Debt, Maturities, Repayments of Principal in Year Ten	0
Long-Term Debt, Maturities, Repayments of Principal after Year Ten	27,000
Long-term Debt, Gross	425,415
Debt Instrument, Unamortized Discount (Premium), Net	(1,271)
Unsecured Debt [Member]
Debt Instrument [Line Items]
2013	95,053
2014	0
2015	300,000
2016	0
2017	450,000
Long-Term Debt, Maturities, Repayments of Principal in Year Six	350,000
Long-Term Debt, Maturities, Repayments of Principal in Year Seven	400,000
Long-Term Debt, Maturities, Repayment of Principal in Year Eight	0
Long-Term Debt, Maturities, Repayment of Principal in Year Nine	315,644
Long-Term Debt, Maturities, Repayments of Principal in Year Ten	300,000
Long-Term Debt, Maturities, Repayments of Principal after Year Ten	0
Long-term Debt, Gross	2,210,697
Debt Instrument, Unamortized Discount (Premium), Net	(16,847)
United Dominion Reality L.P.
Debt Instrument [Line Items]
2013	30,517
2014	22,206
2015	145,199
2016	123,095
2017	62,836
Long-Term Debt, Maturities, Repayments of Principal in Year Six	0
Long-Term Debt, Maturities, Repayments of Principal in Year Seven	0
Long-Term Debt, Maturities, Repayment of Principal in Year Eight	67,310
Long-Term Debt, Maturities, Repayment of Principal in Year Nine	0
Long-Term Debt, Maturities, Repayments of Principal in Year Ten	0
Long-Term Debt, Maturities, Repayments of Principal after Year Ten	27,000
Long-term Debt, Gross	478,163
Debt Instrument, Unamortized Discount (Premium), Net	(2,199)
Total	475,964	$ 927,484
United Dominion Reality L.P. \| Mortgages [Member] \| Fixed Rate Debt
Debt Instrument [Line Items]
2013	30,132
2014	0
2015	0
2016	0
2017	0
Long-Term Debt, Maturities, Repayments of Principal in Year Six	0
Long-Term Debt, Maturities, Repayments of Principal in Year Seven	0
Long-Term Debt, Maturities, Repayment of Principal in Year Eight	0
Long-Term Debt, Maturities, Repayment of Principal in Year Nine	0
Long-Term Debt, Maturities, Repayments of Principal in Year Ten	0
Long-Term Debt, Maturities, Repayments of Principal after Year Ten	0
Total	30,035
United Dominion Reality L.P. \| Fannie Mae credit facilities \| Fixed Rate Debt
Debt Instrument [Line Items]
2013	385
2014	15,640
2015	48,872
2016	123,095
2017	62,836
Long-Term Debt, Maturities, Repayments of Principal in Year Six	0
Long-Term Debt, Maturities, Repayments of Principal in Year Seven	0
Long-Term Debt, Maturities, Repayment of Principal in Year Eight	0
Long-Term Debt, Maturities, Repayment of Principal in Year Nine	0
Long-Term Debt, Maturities, Repayments of Principal in Year Ten	0
Long-Term Debt, Maturities, Repayments of Principal after Year Ten	0
Total	249,298
United Dominion Reality L.P. \| Fannie Mae credit facilities \| Variable Rate Debt
Debt Instrument [Line Items]
2013	0
2014	6,566
2015	96,327
2016	0
2017	0
Long-Term Debt, Maturities, Repayments of Principal in Year Six	0
Long-Term Debt, Maturities, Repayments of Principal in Year Seven	0
Long-Term Debt, Maturities, Repayment of Principal in Year Eight	67,310
Long-Term Debt, Maturities, Repayment of Principal in Year Nine	0
Long-Term Debt, Maturities, Repayments of Principal in Year Ten	0
Long-Term Debt, Maturities, Repayments of Principal after Year Ten	0
Total	169,724
United Dominion Reality L.P. \| Secured Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	27,000
Debt Instrument, Unamortized Discount (Premium), Net	(93)
United Dominion Reality L.P. \| Secured Debt [Member] \| Fixed Rate Debt
Debt Instrument [Line Items]
Long-term Debt, Gross	30,132
Debt Instrument, Unamortized Discount (Premium), Net	(97)
United Dominion Reality L.P. \| Secured Debt [Member] \| Variable Rate Debt
Debt Instrument [Line Items]
Long-term Debt, Gross	250,828
Debt Instrument, Unamortized Discount (Premium), Net	(1,530)
United Dominion Reality L.P. \| Unsecured Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	170,203
Debt Instrument, Unamortized Discount (Premium), Net	(479)
United Dominion Reality L.P. \| Tax-exempt secured notes payable \| Variable Rate Debt
Debt Instrument [Line Items]
2013	0
2014	0
2015	0
2016	0
2017	0
Long-Term Debt, Maturities, Repayments of Principal in Year Six	0
Long-Term Debt, Maturities, Repayments of Principal in Year Seven	0
Long-Term Debt, Maturities, Repayment of Principal in Year Eight	0
Long-Term Debt, Maturities, Repayment of Principal in Year Nine	0
Long-Term Debt, Maturities, Repayments of Principal in Year Ten	0
Long-Term Debt, Maturities, Repayments of Principal after Year Ten	27,000
Total	$ 26,907

Long-Term Debt, Maturities, Repayment of Principal in Year Eight

No definition available.

Name:	udr_LongTermDebtMaturitiesRepaymentofPrincipalinYearEight
Namespace Prefix:	udr_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Long-Term Debt, Maturities, Repayment of Principal in Year Nine

+ References

No definition available.

+ Details

Name:	udr_LongTermDebtMaturitiesRepaymentofPrincipalinYearNine
Namespace Prefix:	udr_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Long-Term Debt, Maturities, Repayments of Principal after Year Ten

+ References

No definition available.

+ Details

Name:	udr_LongTermDebtMaturitiesRepaymentsofPrincipalafterYearTen
Namespace Prefix:	udr_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Long-Term Debt, Maturities, Repayments of Principal in Year Seven

+ References

No definition available.

+ Details

Name:	udr_LongTermDebtMaturitiesRepaymentsofPrincipalinYearSeven
Namespace Prefix:	udr_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Long-Term Debt, Maturities, Repayments of Principal in Year Six

+ References

No definition available.

+ Details

Name:	udr_LongTermDebtMaturitiesRepaymentsofPrincipalinYearSix
Namespace Prefix:	udr_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Long-Term Debt, Maturities, Repayments of Principal in Year Ten

+ References

No definition available.

+ Details

Name:	udr_LongTermDebtMaturitiesRepaymentsofPrincipalinYearTen
Namespace Prefix:	udr_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of long-term debt before deduction of unamortized discount or premium. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt, with initial maturities beyond one year or the normal operating cycle, if longer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 22
-Article 5

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 20
-Article 5

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
-Paragraph 16
-Article 9

+ Details

Name:	us-gaap_DebtInstrumentCarryingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of debt discount (net of debt premium) that was originally recognized at the issuance of the instrument that has yet to be amortized.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28567-108399

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 1A
-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28541-108399

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=34725769&loc=d3e28878-108400

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28551-108399

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28555-108399

+ Details

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

- Definition

Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 3
-Subparagraph (SX 210.12-04.(a))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24072-122690

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6802200&loc=d3e1835-112601

+ Details

Name:	us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6802200&loc=d3e1835-112601

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 3
-Subparagraph (SX 210.12-04.(a))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24072-122690

+ Details

Name:	us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the fourth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

+ Details

Name:	us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the third fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

+ Details

Name:	us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the second fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

+ Details

Name:	us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Carrying value as of the balance sheet date, including the current and noncurrent portions, of collateralized debt obligations (with maturities initially due after one year or beyond the operating cycle, if longer). Such obligations include mortgage loans, chattel loans, and any other borrowings secured by assets of the borrower.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.16)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.16)
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 19, 20, 22
-Article 5

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
-Paragraph 16
-Article 9

+ Details

Name:	us-gaap_SecuredDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_SecuredDebtMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=udr_FixedRateDebtMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=udr_VariableRateDebtMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_UnsecuredDebtMember
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:	us-gaap_LongtermDebtTypeAxis=us-gaap_MortgagesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_LineOfCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=udr_TaxExemptNotesPayableMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: