SECURED AND UNSECURED DEBT, NET - Credit Facilities (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Summary of short-term bank borrowings under unsecured commercial bank credit facility
Borrowings outstanding at end of period	$ 2,900	$ 2,900
Unsecured Commercial Bank Credit Facility
Summary of short-term bank borrowings under unsecured commercial bank credit facility
Total revolving credit facility	2,000,000
Unsecured Revolving credit facility due 2023 | Unsecured Commercial Bank Credit Facility
Summary of short-term bank borrowings under unsecured commercial bank credit facility
Total revolving credit facility	1,100,000
Term Loan due September 2023 | Unsecured Commercial Bank Credit Facility
Summary of short-term bank borrowings under unsecured commercial bank credit facility
Total revolving credit facility	350,000
Revolving Credit Facility | Unsecured Commercial Bank Credit Facility
Summary of short-term bank borrowings under unsecured commercial bank credit facility
Total revolving credit facility	1,100,000	1,100,000
Weighted average daily borrowings during the period ended	56,350	55
Maximum daily borrowings during the period ended	$ 375,000	$ 20,000
Weighted average interest rate during the period ended	1.40%	2.60%
Unsecured Working Capital Credit Facility
Summary of short-term bank borrowings under unsecured commercial bank credit facility
Total revolving credit facility	$ 75,000	$ 75,000
Borrowings outstanding at end of period	22,086	16,583
Weighted average daily borrowings during the period ended	21,503	23,487
Maximum daily borrowings during the period ended	$ 54,974	$ 66,170
Weighted average interest rate during the period ended	1.50%	3.10%
Interest rate at the end of the period	1.00%	2.60%
Unsecured Commercial Paper | United Dominion Realty L.P.
Summary of short-term bank borrowings under unsecured commercial bank credit facility
Borrowings outstanding at end of period	$ 230,000	$ 300,000