Notes Payable, Unsecured Notes and Credit Facility (Details 2) (USD $)	3 Months Ended
	Mar. 31, 2015 extension		Dec. 31, 2014		Mar. 31, 2014
Notes Payable, Unsecured Notes and Credit Facility
Number of operating apartment communities	254
Variable rate unsecured credit facility	$ 0		$ 0
Mortgage notes payable
Notes Payable, Unsecured Notes and Credit Facility
Amount drawn	1,046,799,000		1,047,461,000
Fixed rate notes	2,396,479,000	[1]	2,400,677,000	[1]
Mortgage notes payable held by wholly owned subsidiaries guaranteed by the Company	257,763,000
Variable Rate Unsecured Term Loan [Member]
Notes Payable, Unsecured Notes and Credit Facility
Amount drawn	300,000,000		250,000,000
Unsecured notes
Notes Payable, Unsecured Notes and Credit Facility
Fixed rate notes	2,750,000,000	[2]	2,750,000,000	[2]
Term Loan
Notes Payable, Unsecured Notes and Credit Facility
Principal amount of notes issued					300,000,000
Additional amount with option to draw	50,000,000
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
Period of borrowing rate assumed	1 month
Annual facility fee	1,950,000
Variable rate unsecured credit facility	0		0
Outstanding balance of letters of credit	45,069,000		49,407,000
Net carrying value of apartment communities and improved land parcels securing debt	$ 4,331,683,000
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	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 variable rate	LIBOR
LIBOR | Variable rate unsecured credit facility
Notes Payable, Unsecured Notes and Credit Facility
Debt instrument, basis spread on variable rate (as a percent)	1.05%
Current interest rate (as a percent)	1.23%

[1] Balances at March 31, 2015 and December 31, 2014 exclude $75,544 and $84,449 of debt premium, respectively, as reflected in mortgage notes payable on the Company’s Condensed Consolidated Balance Sheets.

[2] Balances at March 31, 2015 and December 31, 2014 exclude $6,491 and $6,735 of debt discount, respectively, as reflected in unsecured notes, net on the Company’s Condensed Consolidated Balance Sheets.