Real Estate Owned (Details Textual) (USD $)	3 Months Ended	12 Months Ended			9 Months Ended	2 Months Ended
	Sep. 30, 2014	Dec. 31, 2014 Apartment_Homes Communities	Dec. 31, 2013	Dec. 31, 2012	Sep. 30, 2014	Feb. 19, 2015	Jun. 30, 2013
Real Estate Properties [Line Items]
Document Period End Date		Dec. 31, 2014
Real Estate Owned (Textual) [Abstract]
Number of apartment homes owned and consolidated by the Company		39,851
Communities Sold		9
Apartment Homes Sold		2,500	914	6,507
Deferred Gain on Sale of Property		$ 24,683,000	$ 25,400,000
Joint venture, number of homes in communities		10,055
Property, Plant and Equipment, Additions			129,400,000
Number of apartment homes acquired	358
Acquisition-related costs		400,000	100,000	2,300,000
Number of Real Estate Properties		2
Number of States in which Entity Operates		10
Number of Communities Acquired	2
Other Cost and Expense, Operating		8,271,000	7,136,000	5,718,000
Proceeds from Sale of Property, Plant, and Equipment		328,400,000	81,100,000	609,400,000
Payments for (Proceeds from) Investments		(383,886,000)	(250,043,000)	(593,167,000)
Gain (Loss) on Disposition of Property Plant Equipment		138,600,000
Noncash or Part Noncash Acquisition, Debt Assumed		0	63,595,000	34,412,000
Consolidated Joint Venture One [Member]
Real Estate Owned (Textual) [Abstract]
Property, Plant and Equipment, Additions			129,400,000
Number of Communities Acquired			2
Unconsolidated Joint Venture Vitruvian Park [Member]
Real Estate Owned (Textual) [Abstract]
Equity method investment, ownership percent			50.00%				50.00%
Communities Sold			5
Land Sold, Acres			28.4
Deferred Gain on Sale of Property			436,000
Proceeds from Real Estate and Real Estate Joint Ventures			141,300,000
Transaction costs of selling interest in partnerships			936,000
Texas JV
Real Estate Owned (Textual) [Abstract]
Deferred Gain on Sale of Property		23,900,000	24,000,000
Joint Venture Number of Operating Communities Owned				2
Payments to acquire businesses and interest in affiliates				11,700,000
Unconsolidated Joint Venture 399 Fremont [Member]
Real Estate Owned (Textual) [Abstract]
Equity method investment, ownership percent			49.00%
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners			49.00%
Proceeds from Issuance or Sale of Equity			29,900,000
Purchase Obligation			318,000,000
Operating Community [Member]
Real Estate Owned (Textual) [Abstract]
Communities Sold		1
Gain (Loss) on Disposition of Property Plant Equipment		142,500,000
Operating Community [Member] | Unconsolidated Joint Venture Vitruvian Park [Member]
Real Estate Owned (Textual) [Abstract]
Equity method investment, ownership percent		50.00%	50.00%
Number of Units in Real Estate Property		1,394
Number of Real Estate Properties		3	2
Operating Community [Member] | Texas JV
Real Estate Owned (Textual) [Abstract]
Equity method investment, ownership percent		20.00%	20.00%
Number of Units in Real Estate Property		3,359
Number of Real Estate Properties		8		10
Development Community [Member] | Unconsolidated Joint Venture 399 Fremont [Member]
Real Estate Owned (Textual) [Abstract]
Number of Units in Real Estate Property			447
Land
Real Estate Owned (Textual) [Abstract]
Gain (Loss) on Disposition of Property Plant Equipment		1,100,000
Land | Unconsolidated Joint Venture Vitruvian Park [Member]
Real Estate Owned (Textual) [Abstract]
Number of Real Estate Properties		6
New York Properties [Member]
Real Estate Properties [Line Items]
Impairment of Long-Lived Assets Held-for-use			0	9,000,000
Real Estate Owned (Textual) [Abstract]
Number of Communities Owned				3
Number of Apartments Owned				1,706
Other Cost and Expense, Operating				10,400,000
Hurricane Sandy [Member]
Real Estate Owned (Textual) [Abstract]
Total Estimated Insurance Recovery				14,500,000
Lightbox [Member]
Real Estate Owned (Textual) [Abstract]
Property, Plant and Equipment, Additions					45,500,000
Waterscape [Member]
Real Estate Owned (Textual) [Abstract]
Property, Plant and Equipment, Additions					75,200,000
Graybar [Member]
Real Estate Owned (Textual) [Abstract]
Property, Plant and Equipment, Additions					32,200,000
Operating Community [Member]
Real Estate Owned (Textual) [Abstract]
Payments for (Proceeds from) Investments		(324,400,000)
Land
Real Estate Owned (Textual) [Abstract]
Property, Plant and Equipment, Additions					77,800,000
Development Community [Member] | Unconsolidated Joint Venture Vitruvian Park [Member]
Real Estate Owned (Textual) [Abstract]
Communities Sold			1
Apartment Homes Sold			391
13th & Market [Member]
Real Estate Owned (Textual) [Abstract]
Equity method investment, ownership percent		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
Real Estate Owned (Textual) [Abstract]
Equity method investment, ownership percent		50.00%
Proceeds from Sale of Property, Plant, and Equipment		8,300,000
Gain (Loss) on Disposition of Property Plant Equipment		2,200,000
Unconsolidated Joint Venture 399 Fremont [Member]
Real Estate Owned (Textual) [Abstract]
Proceeds from Sale of Property, Plant, and Equipment			29,900,000
Operating Community [Member] | Unconsolidated Joint Venture Vitruvian Park [Member]
Real Estate Owned (Textual) [Abstract]
Communities Sold			2
Apartment Homes Sold			739
Subsequent Event [Member]
Real Estate Owned (Textual) [Abstract]
Square Footage						120,000
Subsequent Event [Member] | Texas JV
Real Estate Owned (Textual) [Abstract]
Communities Sold						8
Proceeds from Sale of Property, Plant, and Equipment						43,500,000
Gain (Loss) on Disposition of Property Plant Equipment						59,100,000
Subsequent Event [Member] | Office Building [Member]
Real Estate Owned (Textual) [Abstract]
Property, Plant and Equipment, Additions						$ 24,000,000
Subsequent Event [Member] | UDR, Inc.
Real Estate Owned (Textual) [Abstract]
Square Footage						44,000