Notes Payable, Unsecured Notes and Credit Facility (Details 3) (USD $)	12 Months Ended
	Dec. 31, 2014 item	Dec. 31, 2013
Notes Payable, Unsecured Notes and Credit Facility
Variable rate unsecured credit facility	$ 0	$ 0
Mortgage notes payable
Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable held by wholly owned subsidiaries guaranteed by the Company	257,917,000
Variable rate unsecured credit facility
Notes Payable, Unsecured Notes and Credit Facility
Available borrowing capacity	1,300,000,000
Line of credit facility, extension period	1 year
Number of extension options	2
Extension period under each option	6 months
Extension fee	1,950,000
Debt instrument, basis spread on variable rate (as a percent)	1.05%
Current interest rate (as a percent)	1.22%
Period of borrowing rate assumed	1 month
Annual facility fee	1,950,000
Outstanding balance of letters of credit	49,407,000	65,018,000
Variable rate unsecured credit facility	0	0
Net carrying value of apartment communities and improved land parcels securing debt	$ 4,413,855,000
Fixed rate mortgage notes payable
Notes Payable, Unsecured Notes and Credit Facility
Weighted average interest rate, debt (as a percent)	4.50%	4.50%
Variable rate mortgage notes payable, unsecured term loan and Credit Facility
Notes Payable, Unsecured Notes and Credit Facility
Weighted average interest rate, debt (as a percent)	1.80%	1.80%
LIBOR | Term loan | Unsecured notes
Notes Payable, Unsecured Notes and Credit Facility
Debt instrument variable rate (as a percent)	LIBOR
Debt instrument, basis spread on variable rate (as a percent)	1.45%
LIBOR | Secured Mortgage
Notes Payable, Unsecured Notes and Credit Facility
Debt instrument, basis spread on variable rate (as a percent)	2.00%
MVPI LLC | Mortgage notes payable
Notes Payable, Unsecured Notes and Credit Facility
Debt instrument variable rate (as a percent)	LIBOR
Debt instrument, basis spread on variable rate (as a percent)	2.50%