Fair Value (Details 2) (Recurring basis, USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Quoted Prices in Active Markets for Identical Assets (Level 1)
Financial Instruments Measured/Discussed at Fair Value
DownREIT units	$ (1,226)	$ (887)
Indebtedness	(2,874,147)	(2,657,143)
Total	(2,875,373)	(2,658,030)
Significant Other Observable Inputs (Level 2)
Financial Instruments Measured/Discussed at Fair Value
Indebtedness	(3,683,875)	(3,637,705)
Total	(3,683,767)	(3,637,599)
Significant Unobservable Inputs (Level 3)
Financial Instruments Measured/Discussed at Fair Value
Total	(11,104)	(15,998)
Significant Unobservable Inputs (Level 3) \| Puts
Financial Instruments Measured/Discussed at Fair Value
Fair value of remaining outstanding Puts	(11,104)	(15,998)
Cash Flow Hedges \| Significant Other Observable Inputs (Level 2) \| Interest Rate Caps
Financial Instruments Measured/Discussed at Fair Value
Derivative assets	58
Total Fair Value
Financial Instruments Measured/Discussed at Fair Value
DownREIT units	(1,226)	(887)
Indebtedness	(6,558,022)	(6,294,848)
Total	(6,570,244)	(6,311,627)
Total Fair Value \| Puts
Financial Instruments Measured/Discussed at Fair Value
Fair value of remaining outstanding Puts	(11,104)	(15,998)
Total Fair Value \| Cash Flow Hedges \| Interest Rate Caps
Financial Instruments Measured/Discussed at Fair Value
Derivative assets	58
Non-designated Hedges \| Significant Other Observable Inputs (Level 2) \| Interest Rate Caps
Financial Instruments Measured/Discussed at Fair Value
Derivative assets	50	106
Non-designated Hedges \| Total Fair Value \| Interest Rate Caps
Financial Instruments Measured/Discussed at Fair Value
Derivative assets	$ 50	$ 106

Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

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The aggregate fair value as of the reporting date of all noncontrolling interests which are redeemable by the (parent) entity (1) at a fixed or determinable price on a fixed or determinable date, (2) at the option of the holder of the noncontrolling interest, or (3) upon occurrence of an event that is not solely within the control of the (parent) entity. This item includes noncontrolling interest holder's ownership (or holders' ownership) regardless of the type of equity interest (common, preferred, other) including all potential organizational (legal) forms of the investee entity.

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