Number of Communities Encumbered.

No definition available.

Name:	udr_NumberOfCommunitiesEncumbered
Namespace Prefix:	udr_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Secured debt including debt on real estate held for sale.

+ References

No definition available.

+ Details

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

- Definition

Unsecured short-term debt instrument issued by corporations which are highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three-years ago does not become a cash equivalent when its remaining maturity is three months.

+ References

No definition available.

+ Details

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

- Definition

The average effective interest rate during the reporting period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=119993939&loc=d3e28551-108399

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

Name:	us-gaap_DebtInstrumentInterestRateDuringPeriod
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentTerm
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount, after accumulated amortization, of debt discount.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 1A
-URI http://asc.fasb.org/extlink&oid=119993939&loc=d3e28541-108399

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=114775985&loc=d3e28878-108400

+ Details

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

- Definition

Amount of unamortized debt discount (premium) and debt issuance costs.

+ References

+ Details

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

- Definition

Amount, after accumulated amortization, of debt premium.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=114775985&loc=d3e28878-108400

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 1A
-URI http://asc.fasb.org/extlink&oid=119993939&loc=d3e28541-108399

+ Details

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

- References

No definition available.

+ Details

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

- Definition

Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

+ References

+ Details

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

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References

Reference 1: 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(22))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-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=120398452&loc=d3e534808-122878

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-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=120400017&loc=d3e572229-122910

+ Details

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

- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)(3)
-URI http://asc.fasb.org/extlink&oid=120520924&loc=SL6031897-161870

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16))
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-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=120398452&loc=d3e534808-122878

Reference 4: 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(22))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

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

- Definition

Including the current and noncurrent portions, carrying value as of the balance sheet date of Notes with the highest claim on the assets of the issuer in case of bankruptcy or liquidation (with maturities initially due after one year or beyond the operating cycle if longer). Senior note holders are paid off in full before any payments are made to junior note holders.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.16(a))
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-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=120398452&loc=d3e534808-122878

+ Details

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

- Definition

Including the current and noncurrent portions, carrying value as of the balance sheet date of uncollateralized debt obligations (with maturities initially due after one year or beyond the operating cycle if longer).

+ References

Reference 1: 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(22))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-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=120398452&loc=d3e534808-122878

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16))
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

+ Details

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

SECURED AND UNSECURED DEBT, NET - Summary (Details) $ in Thousands	1 Months Ended	9 Months Ended
	Feb. 29, 2020 USD ($)	Sep. 30, 2020 USD ($) community	Dec. 31, 2019 USD ($)
Secured debt instruments
Unamortized net premium		$ 16,200	$ 35,300
Interest rate at end of the period		3.01%
Long-term Debt		$ 4,917,646	4,707,524
Unsecured Debt		3,984,559	3,558,083
Borrowings outstanding		$ 2,900	2,900
Weighted Average
Secured debt instruments
Years to maturity		7 years 7 months 6 days
Commercial Paper
Secured debt instruments
Borrowings outstanding at end of period		$ 230,000	300,000
Mortgages Note Payable \| Fixed Rate Debt
Secured debt instruments
Principal outstanding		$ 892,291	884,869
Interest rate at end of the period		3.36%
Number of Communities Encumbered \| community		13
Mortgages Note Payable \| Fixed Rate Debt \| Weighted Average
Secured debt instruments
Years to maturity		7 years 1 month 6 days
Tax-exempt secured notes payable \| Variable Rate Debt
Secured debt instruments
Principal outstanding		$ 27,000	27,000
Interest rate at end of the period		0.77%
Number of Communities Encumbered \| community		1
Tax-exempt secured notes payable \| Variable Rate Debt \| Weighted Average
Secured debt instruments
Years to maturity		11 years 6 months
Credit facilities \| Fixed Rate Debt
Secured debt instruments
Principal outstanding			204,590
Secured Debt
Secured debt instruments
Principal outstanding		$ 933,087	1,149,441
Interest rate at end of the period		3.28%
Long-term Debt		$ 933,087
Number of Communities Encumbered \| community		14
Secured Debt \| Weighted Average
Secured debt instruments
Years to maturity		7 years 3 months 18 days
Secured Debt \| Fixed Rate Debt
Secured debt instruments
Principal outstanding		$ 906,157	1,122,505
Interest rate at end of the period		3.36%
Long-term Debt		$ 906,157
Number of Communities Encumbered \| community		13
Deferred financing costs and other non-cash adjustments		$ (13,866)	(33,046)
Secured Debt \| Fixed Rate Debt \| Weighted Average
Secured debt instruments
Years to maturity		7 years 1 month 6 days
Secured Debt \| Variable Rate Debt
Secured debt instruments
Principal outstanding		$ 26,930	26,936
Interest rate at end of the period		0.77%
Long-term Debt		$ 26,930
Number of Communities Encumbered \| community		1
Deferred finance costs, net		$ (70)	(64)
Secured Debt \| Variable Rate Debt \| Weighted Average
Secured debt instruments
Years to maturity		11 years 6 months
Unsecured Revolving credit facility due 2023 \| Weighted Average
Secured debt instruments
Years to maturity		2 years 3 months 18 days
Unsecured Revolving credit facility due 2020 \| Commercial Paper
Secured debt instruments
Interest rate at end of the period		0.30%
Borrowings outstanding at end of period		$ 230,000	300,000
Unsecured Revolving credit facility due 2020 \| Commercial Paper \| Weighted Average
Secured debt instruments
Years to maturity		1 month 6 days
Unsecured Working Capital Credit Facility
Secured debt instruments
Interest rate at end of the period		0.97%
Borrowings outstanding		$ 22,086	16,583
Unsecured Working Capital Credit Facility \| Weighted Average
Secured debt instruments
Years to maturity		1 year 3 months 18 days
Term Loan due September 2023
Secured debt instruments
Interest rate at end of the period		1.06%
Senior Notes		$ 35,000	35,000
Term Loan due September 2023 \| Weighted Average
Secured debt instruments
Years to maturity		3 years
Term Loan due September 2023 \| Fixed Rate Debt
Secured debt instruments
Interest rate at end of the period		2.55%
Senior Notes		$ 315,000	315,000
Term Loan due September 2023 \| Fixed Rate Debt \| Weighted Average
Secured debt instruments
Years to maturity		3 years
3.75% Medium-Term Notes Due July 2024
Secured debt instruments
Unamortized discount		$ 239	470
Interest rate at end of the period		3.69%
Senior Notes		$ 182,867	299,530
3.75% Medium-Term Notes Due July 2024 \| Weighted Average
Secured debt instruments
Years to maturity		3 years 9 months 18 days
8.50% Debentures, Due September 2024
Secured debt instruments
Interest rate at end of the period		8.50%
Senior Notes		$ 15,644	15,644
8.50% Debentures, Due September 2024 \| Weighted Average
Secured debt instruments
Years to maturity		4 years
4.00% Medium-Term Note due October 2025
Secured debt instruments
Unamortized discount		$ 344	396
Interest rate at end of the period		4.53%
Senior Notes		$ 299,656	299,604
4.00% Medium-Term Note due October 2025 \| Weighted Average
Secured debt instruments
Years to maturity		5 years
2.95% Medium-Term Note due September 2026
Secured debt instruments
Interest rate at end of the period		2.95%
Senior Notes		$ 300,000	300,000
2.95% Medium-Term Note due September 2026 \| Weighted Average
Secured debt instruments
Years to maturity		5 years 10 months 24 days
3.50 Medium-Term Note due July 2027
Secured debt instruments
Unamortized discount		$ 476	529
Interest rate at end of the period		3.50%
Senior Notes		$ 299,524	299,471
3.50 Medium-Term Note due July 2027 \| Weighted Average
Secured debt instruments
Years to maturity		6 years 9 months 18 days
3.50% Medium-Term Notes Due January 2028
Secured debt instruments
Unamortized discount		$ 865	954
Interest rate at end of the period		3.50%
Senior Notes		$ 299,135	299,046
3.50% Medium-Term Notes Due January 2028 \| Weighted Average
Secured debt instruments
Years to maturity		7 years 3 months 18 days
4.40% Medium-Term Notes due January 2029
Secured debt instruments
Unamortized discount		$ 5	5
Interest rate at end of the period		4.27%
Senior Notes		$ 299,995	299,995
4.40% Medium-Term Notes due January 2029 \| Weighted Average
Secured debt instruments
Years to maturity		8 years 3 months 18 days
3.20% Medium-Term Notes due January 2030
Secured debt instruments
Unamortized discount		$ 12,756	2,281
Interest rate at end of the period	3.32%	3.32%
Senior Notes	$ 600,000	$ 612,756	402,281
3.20% Medium-Term Notes due January 2030 \| Weighted Average
Secured debt instruments
Years to maturity		9 years 3 months 18 days
3.00% Medium-Term Notes due August 2031
Secured debt instruments
Unamortized discount		$ 1,051	1,123
Interest rate at end of the period		3.01%
Senior Notes		$ 398,949	398,877
3.00% Medium-Term Notes due August 2031 \| Weighted Average
Secured debt instruments
Years to maturity		10 years 10 months 24 days
2.10% Medium Term Note Due August 1, 2032
Secured debt instruments
Unamortized discount		$ 417	0
Interest rate at end of the period		2.10%
Senior Notes		$ 399,583
2.10% Medium Term Note Due August 1, 2032 \| Weighted Average
Secured debt instruments
Years to maturity		11 years 9 months 18 days
3.10% Medium-Term Notes due November 2034
Secured debt instruments
Unamortized discount		$ 1,243	1,309
Interest rate at end of the period		3.13%
Senior Notes		$ 298,757	298,691
3.10% Medium-Term Notes due November 2034 \| Weighted Average
Secured debt instruments
Years to maturity		14 years 1 month 6 days
Other
Secured debt instruments
Senior Notes		$ 11	13
Unsecured Debt
Secured debt instruments
Interest rate at end of the period		3.08%
Long-term Debt		$ 3,984,559
Unsecured Debt		3,984,559	3,558,083
Deferred finance costs, net		$ (24,404)	(21,652)
Unsecured Debt \| Weighted Average
Secured debt instruments
Years to maturity		7 years 8 months 12 days
United Dominion Realty L.P.
Secured debt instruments
Interest rate at end of the period		2.52%
Long-term Debt		$ 99,093	99,071
Number of Communities Encumbered \| community		2
United Dominion Realty L.P. \| Weighted Average
Secured debt instruments
Years to maturity		9 years 10 months 24 days
United Dominion Realty L.P. \| Fixed Rate Debt
Secured debt instruments
Interest rate at end of the period		3.10%
Long-term Debt		$ 72,163	72,135
Number of Communities Encumbered \| community		1
United Dominion Realty L.P. \| Fixed Rate Debt \| Weighted Average
Secured debt instruments
Years to maturity		9 years 3 months 18 days
United Dominion Realty L.P. \| Variable Rate Debt
Secured debt instruments
Interest rate at end of the period		0.77%
Long-term Debt		$ 26,930	26,936
Number of Communities Encumbered \| community		1
Deferred finance costs, net		$ (70)	(64)
United Dominion Realty L.P. \| Variable Rate Debt \| Weighted Average
Secured debt instruments
Years to maturity		11 years 6 months
United Dominion Realty L.P. \| Mortgages Note Payable
Secured debt instruments
Principal outstanding		$ 72,500
United Dominion Realty L.P. \| Mortgages Note Payable \| Fixed Rate Debt
Secured debt instruments
Principal outstanding		$ 72,500	72,500
Interest rate at end of the period		3.10%
Number of Communities Encumbered \| community		1
Deferred finance costs, net		$ (337)	(365)
United Dominion Realty L.P. \| Mortgages Note Payable \| Fixed Rate Debt \| Weighted Average
Secured debt instruments
Years to maturity		9 years 3 months 18 days
United Dominion Realty L.P. \| Tax-exempt secured notes payable \| Variable Rate Debt
Secured debt instruments
Principal outstanding		$ 27,000	$ 27,000
Interest rate at end of the period		0.77%
Number of Communities Encumbered \| community		1
United Dominion Realty L.P. \| Tax-exempt secured notes payable \| Variable Rate Debt \| Weighted Average
Secured debt instruments
Years to maturity		11 years 6 months