SECURED AND UNSECURED DEBT, NET - Debt Covenants (Details) $ in Thousands			1 Months Ended				12 Months Ended
	Jul. 02, 2019 USD ($)	Oct. 20, 2015	Nov. 30, 2019 USD ($) community loan item	Oct. 30, 2019 USD ($)	Aug. 31, 2019 USD ($)	Jul. 31, 2019 USD ($)	Dec. 31, 2019 USD ($) item community	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Fixed and variable rate debt
Amortization of financing costs							$ 4,200	$ 4,200
Secured Debt
Secured debt amount which encumbers real estate owned based upon book value							$ 2,100,000
Percentage of secured debt which encumbers real estate owned based upon book value							16.80%
Secured debt amount of real estate owned which is unencumbered							$ 10,500,000
Percentage of secured debt of real estate owned which is unencumbered							83.20%
Number of Extensions of loan | item							2
Interest rate at end of the period							3.43%
Long term debt fair value			$ 551,800
Extension period of option on loan		6 months
Borrowings outstanding at end of period							$ 2,900	3,300
Unamortized net premium							$ 35,300	5,000
UDR/MetLife operating communities
Secured Debt
Debt instrument, number of mortgage notes payable | item			6
Equity Method Investment, Ownership Percentage			50.00%
Number of communities acquired | community			10				10
Minimum
Secured Debt
Equity Method Investment, Ownership Percentage							100.00%
Commercial Paper
Secured Debt
Interest rate at end of the period							1.99%
Borrowings outstanding at end of period							$ 300,000	101,115
Fixed Rate Mortgage Due October 2029
Secured Debt
Principal outstanding							$ 90,000
Interest rate at end of the period							2.70%
Mortgage Due February 2030
Secured Debt
Principal outstanding							$ 72,500
Interest rate at end of the period							3.10%
3.20% senior unsecured notes due 2030
Secured Debt
Principal outstanding				$ 400,000
Interest rate at end of the period	3.20%			3.20%
Senior Notes	$ 300,000			$ 100,000
Percentage of notes price				103.32%
3.20% senior unsecured notes due 2030 | Treasury Lock
Secured Debt
Weighted average interest rate (as a percent)				3.24%
3.10% senior unsecured notes due 2034
Secured Debt
Interest rate at end of the period				3.10%
Senior Notes				$ 300,000
Percentage of notes price				99.56%
3.10% senior unsecured notes due 2034 | Treasury Lock
Secured Debt
Weighted average interest rate (as a percent)				3.13%
4.63% Medium-Term Notes due January 2022
Secured Debt
Interest rate at end of the period				4.63%
Make-whole amount				$ 22,000
Senior Notes				$ 400,000
Credit facilities
Secured Debt
Redemption of debt							$ 90,000
Unsecured Debt
Secured Debt
Interest rate at end of the period							3.27%
Basis points added to to variable rate							90.00%
Unsecured Debt | Maximum
Secured Debt
Basis points added to to variable rate							1.65%
Unsecured Debt | Minimum
Secured Debt
Basis points added to to variable rate							0.80%
Unsecured Working Capital Credit Facility due January 2021
Secured Debt
Credit facilities with aggregate commitment							$ 75,000	75,000
Interest rate at end of the period							2.59%
Basis points added to to variable rate							82.50%
Borrowings outstanding at end of period							$ 16,583	16
Unsecured Working Capital Credit Facility due January 2021 | Maximum
Secured Debt
Basis points added to to variable rate							145.00%
Unsecured Working Capital Credit Facility due January 2021 | Minimum
Secured Debt
Basis points added to to variable rate							75.00%
3.75% Medium-Term Notes Due July 2024
Secured Debt
Interest rate at end of the period							3.75%
Portion of medium term note subject to interest rate swaps							$ 100,000
Long-term Debt, Weighted Average Interest Rate							3.69%
Senior Notes							$ 299,530	299,426
Mortgages Notes Payable
Secured Debt
Long term debt fair value			$ 332,500
Debt instrument, number of mortgage notes payable | loan			6
Mortgages Notes Payable | UDR/MetLife operating communities
Secured Debt
Equity Method Investment, Ownership Percentage			50.00%
Number of communities acquired | community			6
Mortgages Notes Payable | Maximum
Secured Debt
Principal outstanding			$ 94,100
Interest rate			4.12%
Interest rate of medium-term notes			4.12%
Mortgages Notes Payable | Minimum
Secured Debt
Principal outstanding			$ 32,600
Interest rate			3.25%
Interest rate of medium-term notes			3.25%
Mortgages Notes Payable | Fixed Rate Debt
Secured Debt
Principal outstanding			$ 313,400				$ 884,869	417,989
Interest rate at end of the period							3.61%
Mortgages Notes Payable | Fixed Rate Debt | Maximum
Secured Debt
Notes payable maximum interest rates range							4.35%
Mortgages Notes Payable | Fixed Rate Debt | Minimum
Secured Debt
Notes payable maximum interest rates range							2.70%
Debt Assumed As Part of Acquisition
Secured Debt
Amortization of debt discount (Premium)							$ 3,000	3,000	$ 3,000
Tax-exempt secured notes payable | Variable Rate Debt
Secured Debt
Notes payable maximum interest rates range							1.79%
Principal outstanding							$ 27,000	94,700
Interest rate at end of the period							1.79%
Credit facilities
Secured Debt
Principal outstanding			205,000
Long term debt fair value			$ 219,300
Interest rate			4.90%
Interest rate of medium-term notes			4.90%
Credit facilities | UDR/MetLife operating communities
Secured Debt
Debt instrument, number of mortgage notes payable | community			4
Equity Method Investment, Ownership Percentage			50.00%
Revolving Credit Facility
Secured Debt
Basis points added to to variable rate							82.50%
Commitment fee							15.00%
Revolving Credit Facility | Maximum
Secured Debt
Basis points added to to variable rate							1.45%
Commitment fee							0.30%
Revolving Credit Facility | Minimum
Secured Debt
Basis points added to to variable rate							0.75%
Commitment fee							10.00%
4.00% Medium-Term Note due October 2025
Secured Debt
Interest rate at end of the period							4.00%
Portion of medium term note subject to interest rate swaps							$ 200,000
Long-term Debt, Weighted Average Interest Rate							4.53%
Senior Notes							$ 299,604	299,535
4.40% Medium-Term Notes due January 2029
Secured Debt
Interest rate at end of the period							4.40%
Portion of medium term note subject to interest rate swaps							$ 150,000
Long-term Debt, Weighted Average Interest Rate							4.27%
Senior Notes							$ 299,995	299,994
2.95% Medium-Term Note due September 2026
Secured Debt
Interest rate at end of the period							2.95%
Senior Notes							$ 300,000	300,000
3.20% Medium-Term Notes due January 2030
Secured Debt
Interest rate at end of the period							3.20%
Interest rate						3.20%
Medium-term notes						$ 300,000
Interest rate of medium-term notes						3.20%
Percentage of principal amount at issuance						99.66
Long-term Debt, Weighted Average Interest Rate						3.42%
Senior Notes							$ 402,281
Unamortized net premium							$ 2,281	$ 0
3.00% Medium-Term Notes due August 2031
Secured Debt
Interest rate at end of the period							3.00%
Interest rate					3.00%
Medium-term notes					$ 400,000
Interest rate of medium-term notes					3.00%
Percentage of principal amount at issuance					99.71
Senior Notes							$ 398,877
3.00% Medium-Term Notes due August 2031 | Treasury Lock
Secured Debt
Medium-term notes					$ 150,000
Weighted average interest rate (as a percent)					3.01%
3.70% Term Notes Due October 2020
Secured Debt
Interest rate at end of the period								3.70%
Interest rate					3.70%
Make-whole amount					$ 5,400
Interest rate of medium-term notes					3.70%
Redemption of debt					$ 300,000
Senior Notes								$ 299,986
Unsecured Commercial Bank Credit Facility
Secured Debt
Credit facilities with aggregate commitment							2,000,000
Unsecured Commercial Bank Credit Facility | Unsecured Revolving credit facility due 2023
Secured Debt
Credit facilities with aggregate commitment							1,100,000
Unsecured Commercial Bank Credit Facility | Revolving Credit Facility
Secured Debt
Credit facilities with aggregate commitment							$ 1,100,000	1,100,000
United Dominion Realty L.P.
Secured Debt
Notes payable maximum interest rates range							3.43%
Principal outstanding							$ 99,071	26,929
Interest rate at end of the period							2.78%
United Dominion Realty L.P. | Fixed Rate Debt
Secured Debt
Principal outstanding							$ 72,135
Interest rate at end of the period							3.10%
United Dominion Realty L.P. | Commercial Paper
Secured Debt
Borrowings outstanding at end of period							$ 300,000	101,100
United Dominion Realty L.P. | Mortgages Notes Payable | Fixed Rate Debt
Secured Debt
Principal outstanding							$ 72,500
Interest rate at end of the period							3.10%
Interest rate							3.10%
Interest rate of medium-term notes							3.10%
United Dominion Realty L.P. | Tax-exempt secured notes payable | Variable Rate Debt
Secured Debt
Principal outstanding							$ 27,000	27,000
Interest rate at end of the period							1.79%
Credit facilities
Secured Debt
Borrowings outstanding at end of period							$ 204,590	90,000
Credit facilities | Fixed Rate Debt
Secured Debt
Principal outstanding							$ 204,590	90,000
Interest rate at end of the period							4.90%
Credit facilities | Fair Value, Measurements, Recurring | Carrying Amount
Secured Debt
Principal outstanding							$ 218,490
Credit facilities | Fair Value, Measurements, Recurring | Carrying Amount | Fannie Mae | Fixed Rate Debt
Secured Debt
Principal outstanding								90,000
Mortgages Notes Payable | Tax-exempt secured notes payable | Variable Rate Debt
Secured Debt
Payment of notes payable							67,700
Mortgages Notes Payable | Fair Value, Measurements, Recurring | Carrying Amount | Fixed Rate Debt
Secured Debt
Principal outstanding							$ 906,228	$ 417,989