Fair Value (Details 2) (Recurring basis, USD $) In Thousands, unless otherwise specified	Mar. 31, 2013
Total Fair Value
Financial Instruments Measured/Discussed at Fair Value
DownREIT units	$ (950)
Indebtedness	(6,115,233)
Total	(6,188,042)
Total Fair Value | Puts
Financial Instruments Measured/Discussed at Fair Value
Fair value of remaining outstanding Put	(19,819)
Total Fair Value | Interest Rate Caps
Financial Instruments Measured/Discussed at Fair Value
Derivative assets	29
Total Fair Value | Interest Rate Swaps
Financial Instruments Measured/Discussed at Fair Value
Derivative liabilities	(52,069)
Quoted Prices in Active Markets for Identical Assets (Level 1)
Financial Instruments Measured/Discussed at Fair Value
DownREIT units	(950)
Indebtedness	(1,993,536)
Total	(1,994,486)
Significant Other Observable Inputs (Level 2)
Financial Instruments Measured/Discussed at Fair Value
Indebtedness	(4,121,697)
Total	(4,173,737)
Significant Other Observable Inputs (Level 2) | Interest Rate Caps
Financial Instruments Measured/Discussed at Fair Value
Derivative assets	29
Significant Other Observable Inputs (Level 2) | Interest Rate Swaps
Financial Instruments Measured/Discussed at Fair Value
Derivative liabilities	(52,069)
Significant Unobservable Inputs (Level 3)
Financial Instruments Measured/Discussed at Fair Value
Total	(19,819)
Significant Unobservable Inputs (Level 3) | Puts
Financial Instruments Measured/Discussed at Fair Value
Fair value of remaining outstanding Put	$ (19,819)