Joint Ventures (Details Textual) (USD $)	1 Months Ended	3 Months Ended	12 Months Ended			9 Months Ended	1 Months Ended	3 Months Ended	2 Months Ended
	Jun. 30, 2013	Dec. 31, 2014 Communities Apartment_Homes	Dec. 31, 2014 Communities Apartment_Homes	Dec. 31, 2013	Dec. 31, 2012	Sep. 30, 2014	Jul. 31, 2014	Sep. 30, 2014	Feb. 19, 2015	Jan. 31, 2014	Jan. 31, 2012	Mar. 31, 2014 Communities
Joint Ventures
Real Estate Investment Property, Net		$ 5,770,855,000	$ 5,770,855,000	$ 5,523,029,000
Debt associated with Real estate acquired				63,600,000
Joint venture, number of homes in communities		10,055	10,055
Ownership interest in joint venture purchased				100.00%
Initial investment in equity method investment				80,200,000
Property, Plant and Equipment, Additions				129,400,000
Unamortized discount		6,700,000	6,700,000	11,800,000
First installment of payable incurred in partial consideration for acquisition of ownership interest in joint venture		520,934,000	520,934,000
Second installment of payable incurred in partial consideration for acquisition of ownership interest in joint venture		248,881,000	248,881,000
Interest expense incurred during period			130,454,000	126,083,000	138,792,000
Company's equity investment in joint venture		718,226,000	718,226,000	507,655,000
Ownership interest in underlying assets exchanged	10.00%
Cash paid in equity method investment exchange	15,600,000
Weighted Average Interest Rate		3.94%
Payments to acquire equity method investments			222,930,000	43,291,000	283,369,000
Document Period End Date			Dec. 31, 2014
Deferred gains on the sale of depreciable property		24,683,000	24,683,000	25,400,000
Communities Sold			9
Proceeds from Sale of Property, Plant, and Equipment			328,400,000	81,100,000	609,400,000
Gain (Loss) on Disposition of Property Plant Equipment			138,600,000
Management fees for our involvement in the joint ventures			11,300,000	11,200,000	11,800,000
Deposits										4,000,000
Real Estate Owned Gross		8,383,259,000	8,383,259,000	8,207,977,000
Secured debt		1,361,529,000	1,361,529,000	1,442,077,000
SEC Schedule III, Real Estate, Cost of Real Estate Sold	140,000,000		269,681,000	70,687,000	559,154,000
Percentage of real estate retained in sale of real estate owned				50.00%
Number of Real Estate Properties		139	139
13th & Market and DCP [Member]
Joint Ventures
Property, Plant and Equipment, Additions						24,700,000
Wilshire Crescent Heights [Member]
Joint Ventures
Property, Plant and Equipment, Additions						15,300,000
Land
Joint Ventures
Property, Plant and Equipment, Additions						77,800,000
Denver and San Diego Operating Communities [Member]
Joint Ventures
Equity method investment, ownership percent				50.00%
Number of operating communities in equity method investment exchange	2
Ownership interest acquired in exchange	35.00%
MetLife Swap [Member]
Joint Ventures
Equity method investment, ownership percent				12.00%		50.00%		50.00%
Cash paid in equity method investment exchange							21,500,000	82,500,000
Communities Sold						2
Proceeds from Sale of Property, Plant, and Equipment						3,000,000
13th & Market [Member]
Joint Ventures
Deposits										2,000,000
Unconsolidated Joint Venture Vitruvian Park [Member]
Joint Ventures
Equity method investment, ownership percent	50.00%			50.00%
Company's equity investment in joint venture		80,302,000	80,302,000	79,318,000
Deferred gains on the sale of depreciable property				436,000
Communities Sold				5
Proceeds from Real Estate and Real Estate Joint Ventures				141,300,000
Stated interest rate				4.00%
MetLife I
Joint Ventures
Company's equity investment in joint venture		13,306,000	13,306,000	47,497,000
MetLife II
Joint Ventures
Company's equity investment in joint venture		431,277,000	431,277,000	327,926,000
399 Fremont
Joint Ventures
Initial investment in equity method investment											37,300,000
Ownership percentage				7.50%	7.50%
Company's equity investment in joint venture					55,500,000
Non-controlling interest held in joint venture											92.50%
399 Fremont | 1st payment
Joint Ventures
Payments for interest in joint venture					13,500,000
399 Fremont | 2nd payment
Joint Ventures
Payments for interest in joint venture				4,700,000
Lodge at Stoughton
Joint Ventures
Number of operating communities in joint venture		1	1
Equity method investment, ownership percent				95.00%
Bridge Loan		40,800,000	40,800,000
Number of extension options on loan			2
Extension period of option on loan			3 months
KFH
Joint Ventures
Equity method investment, ownership percent		30.00%	30.00%
Company's equity investment in joint venture		21,596,000	21,596,000	25,919,000
Joint venture investment in multifamily properties		450,000,000	450,000,000
Total equity contribution by partners when fully invested		180,000,000	180,000,000
UDR's equity investment in joint venture when fully invested		54,000,000	54,000,000
Texas JV
Joint Ventures
Ownership interest in joint venture purchased					80.00%
Number of operating communities in joint venture					2
Company's equity investment in joint venture		(25,901,000)	(25,901,000)	(23,591,000)
Payments to acquire businesses and interest in affiliates					11,700,000
Deferred gains on the sale of depreciable property		23,900,000	23,900,000	24,000,000
Texas JV | Subsequent Event [Member]
Joint Ventures
Communities Sold									8
Proceeds from Sale of Property, Plant, and Equipment									43,500,000
Fee Income from the Sale of Real Estate									9,600,000
Gain (Loss) on Disposition of Property Plant Equipment									59,100,000
13th & Market
Joint Ventures
Ownership percentage		0.00%	0.00%	5.00%
Non-controlling interest held in joint venture				95.00%
Orange County, CA
Joint Ventures
Property, Plant and Equipment, Additions				129,400,000
Unconsolidated Joint Venture 399 Fremont [Member]
Joint Ventures
Ownership percentage				49.00%
Purchase Obligation				318,000,000
Proceeds from Issuance or Sale of Equity				29,900,000
Equity method investment, ownership percent				49.00%
Company's equity investment in joint venture				31,100,000
Participating Loan Investment Steele Creek Denver Colorado [Member]
Joint Ventures
Maximum Percentage to Finance		85.00%	85.00%
Line of Credit Facility, Maximum Borrowing Capacity		92,000,000	92,000,000
Weighted average interest rate at the end of the period		6.50%	6.50%
Participating Interest in Investment		50.00%	50.00%
Income from Participating Loan			156,000
Fully Entitled Land [Member] | MetLife I
Joint Ventures
Equity method investment, ownership percent		50.00%	50.00%
Number of Real Estate Properties		1	1
Land
Joint Ventures
Gain (Loss) on Disposition of Property Plant Equipment			1,100,000
Land | Unconsolidated Joint Venture Other MetLife [Member]
Joint Ventures
Number of Real Estate Properties		2	2
Land | Unconsolidated Joint Venture Vitruvian Park [Member]
Joint Ventures
Number of Real Estate Properties		6	6
Land | MetLife I
Schedule of Equity Method Investments [Line Items]
Number of apartments of development community		0	0
Joint Ventures
Equity method investment, ownership percent		5.00%	5.00%
Number of Real Estate Properties		3	3
Land | MetLife II
Joint Ventures
Equity method investment, ownership percent						50.10%		50.10%
Number of Real Estate Properties						2		2
Land | Noncontrolling Interest
Joint Ventures
Equity method investment, ownership percent						49.90%		49.90%
Land | Wilshire at LaJolla [Member]
Joint Ventures
Equity method investment, ownership percent						50.10%		50.10%
Land | Wilshire Crescent Heights [Member]
Joint Ventures
Equity method investment, ownership percent						50.00%		50.00%
Number of Real Estate Properties		1	1
Operating Community [Member]
Joint Ventures
Number of operating communities in equity method investment exchange	4
Communities Sold			1
Gain (Loss) on Disposition of Property Plant Equipment			142,500,000
Operating Community [Member] | Unconsolidated Joint Venture Other MetLife [Member]
Joint Ventures
Number of Units in Real Estate Property		1,282	1,282
Equity method investment, ownership percent		50.60%	50.60%	35.80%
Company's equity investment in joint venture		134,939,000	134,939,000	36,313,000
Number of Real Estate Properties		1	1
Operating Community [Member] | Unconsolidated Joint Venture Vitruvian Park [Member]
Joint Ventures
Number of Units in Real Estate Property		1,394	1,394
Equity method investment, ownership percent		50.00%	50.00%	50.00%
Company's equity investment in joint venture		80,302,000	80,302,000	79,318,000
Number of Real Estate Properties		3	3	2
Operating Community [Member] | MetLife I
Joint Ventures
Number of Units in Real Estate Property		0	0
Equity method investment, ownership percent		15.70%	15.70%	4.50%
Company's equity investment in joint venture		13,306,000	13,306,000	47,497,000
Number of Real Estate Properties		4	4									6
Operating Community [Member] | MetLife II
Joint Ventures
Number of Units in Real Estate Property		4,642	4,642
Equity method investment, ownership percent		50.00%	50.00%	50.00%
Company's equity investment in joint venture		431,277,000	431,277,000	327,926,000
Number of Real Estate Properties		21	21
Operating Community [Member] | KFH
Joint Ventures
Number of Units in Real Estate Property		660	660
Equity method investment, ownership percent		30.00%	30.00%	30.00%
Company's equity investment in joint venture		21,596,000	21,596,000	25,919,000
Number of Real Estate Properties		3	3
Operating Community [Member] | Texas JV
Joint Ventures
Number of Units in Real Estate Property		3,359	3,359
Equity method investment, ownership percent		20.00%	20.00%	20.00%
Company's equity investment in joint venture		(25,901,000)	(25,901,000)	(23,591,000)
Number of Real Estate Properties		8	8		10
Development Community [Member] | Unconsolidated Joint Venture Other MetLife [Member]
Joint Ventures
Number of Real Estate Properties		3	3
Development Community [Member] | Unconsolidated Joint Venture Vitruvian Park [Member]
Joint Ventures
Debt Instrument, Description of Variable Rate Basis	175
Number of extension options on loan	2
Extension period of option on loan	1 year
Development Community [Member] | Unconsolidated Joint Venture 399 Fremont [Member]
Joint Ventures
Number of Units in Real Estate Property				447
Development Community [Member] | Participating Loan Investment Steele Creek Denver Colorado [Member]
Joint Ventures
Number of Units in Real Estate Property		218	218
Company's equity investment in joint venture		62,707,000	62,707,000	14,273,000
Income from Participating Loan			2,350,000	156,000	0
Ownership interest of Company in Partnership [Member]
Joint Ventures
Secured debt				118,300,000
Proceeds from Issuance of Other Long-term Debt	58,700,000
Ownership interest of Company in Partnership [Member] | Unconsolidated Joint Venture Vitruvian Park [Member]
Joint Ventures
Real Estate Owned Gross				145,000,000
Secured debt				62,800,000
Unconsolidated Joint Venture Vitruvian Park [Member] | Operating Community [Member] | Unconsolidated Joint Venture Vitruvian Park [Member]
Joint Ventures
Debt Instrument, Term				2 years
Unconsolidated Joint Venture Vitruvian Park [Member] | Development Community [Member] | Unconsolidated Joint Venture Vitruvian Park [Member]
Joint Ventures
Debt Instrument, Term				10 years
Participating Loan Investment Steele Creek Denver Colorado [Member]
Joint Ventures
Purchase Obligation		108,000,000	108,000,000
Number of Real Estate Properties		1	1
13th & Market [Member]
Joint Ventures
Equity method investment, ownership percent		49.00%	49.00%
Proceeds from Sale of Property, Plant, and Equipment			54,200,000
Gain (Loss) on Disposition of Property Plant Equipment			7,200,000
3033 Wilshire
Joint Ventures
Equity method investment, ownership percent		50.00%	50.00%
Proceeds from Sale of Property, Plant, and Equipment			8,300,000
Gain (Loss) on Disposition of Property Plant Equipment			$ 2,200,000