Fair Value (Details 2) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 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	$ (953)
Indebtedness	(6,018,946)
Total	(6,031,839)
Recurring basis | Total Fair Value | Puts
Financial Instruments Measured/Discussed at Fair Value
Fair value of remaining outstanding Puts	(12,058)
Recurring basis | Total Fair Value | Interest Rate Caps
Financial Instruments Measured/Discussed at Fair Value
Derivative assets	118
Recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1)
Financial Instruments Measured/Discussed at Fair Value
DownREIT units	(953)
Indebtedness	(2,317,364)
Total	(2,318,317)
Recurring basis | Significant Other Observable Inputs (Level 2)
Financial Instruments Measured/Discussed at Fair Value
Indebtedness	(3,701,582)
Total	(3,701,464)
Recurring basis | Significant Other Observable Inputs (Level 2) | Interest Rate Caps
Financial Instruments Measured/Discussed at Fair Value
Derivative assets	118
Recurring basis | Significant Unobservable Inputs (Level 3)
Financial Instruments Measured/Discussed at Fair Value
Total	(12,058)
Recurring basis | Significant Unobservable Inputs (Level 3) | Puts
Financial Instruments Measured/Discussed at Fair Value
Fair value of remaining outstanding Puts	$ (12,058)