Fair Value (Details 2) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2013 item
Puts
Financial Instruments Measured/Discussed at Fair Value
Number of ventures in which the entity is required to purchase interest in the investment at guaranteed minimum amount	3
Puts | Archstone
Financial Instruments Measured/Discussed at Fair Value
Number of ventures in which the entity is required to purchase interest in the investment at guaranteed minimum amount	2
Recurring basis | Total Fair Value
Financial Instruments Measured/Discussed at Fair Value
DownREIT units	$ (1,012)
Indebtedness	(5,868,176)
Total	(5,887,207)
Recurring basis | Total Fair Value | Puts
Financial Instruments Measured/Discussed at Fair Value
Fair value of remaining outstanding Puts	(18,067)
Recurring basis | Total Fair Value | Interest Rate Caps
Financial Instruments Measured/Discussed at Fair Value
Derivative assets	48
Recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1)
Financial Instruments Measured/Discussed at Fair Value
DownREIT units	(1,012)
Indebtedness	(1,920,035)
Total	(1,921,047)
Recurring basis | Significant Other Observable Inputs (Level 2)
Financial Instruments Measured/Discussed at Fair Value
Indebtedness	(3,948,141)
Total	(3,948,093)
Recurring basis | Significant Other Observable Inputs (Level 2) | Interest Rate Caps
Financial Instruments Measured/Discussed at Fair Value
Derivative assets	48
Recurring basis | Significant Unobservable Inputs (Level 3) | Puts
Financial Instruments Measured/Discussed at Fair Value
Fair value of remaining outstanding Puts	$ (18,067)