Notes Payable, Unsecured Notes and Credit Facility (Details 2) (USD $)	3 Months Ended		9 Months Ended			1 Months Ended					1 Months Ended								1 Months Ended		9 Months Ended						9 Months Ended
	Sep. 30, 2014 community	Sep. 30, 2013	Sep. 30, 2014 community	Sep. 30, 2013	Dec. 31, 2013	Jun. 30, 2014 Mortgage notes payable	Sep. 30, 2014 Mortgage notes payable community		Dec. 31, 2013 Mortgage notes payable		Apr. 30, 2014 Unsecured notes	Sep. 30, 2014 Unsecured notes		Dec. 31, 2013 Unsecured notes		Sep. 30, 2014 Term Loan	Mar. 31, 2014 Term Loan	Apr. 30, 2014 Secured Mortgage	Jun. 30, 2014 Notes payable maturing in 2015 Mortgage notes payable	Sep. 30, 2014 Notes payable maturing in 2015 Mortgage notes payable	Sep. 30, 2014 Variable rate unsecured credit facility extension	Dec. 31, 2013 Variable rate unsecured credit facility	Sep. 30, 2014 Fixed rate mortgage notes payable	Dec. 31, 2013 Fixed rate mortgage notes payable	Sep. 30, 2014 Variable rate mortgage notes payable, unsecured term loan and Credit Facility	Dec. 31, 2013 Variable rate mortgage notes payable, unsecured term loan and Credit Facility	Sep. 30, 2014 LIBOR Term Loan Unsecured notes	Sep. 30, 2014 LIBOR Secured Mortgage	Sep. 30, 2014 LIBOR Variable rate unsecured credit facility
Notes Payable, Unsecured Notes and Credit Facility
Principal amount of notes issued																$ 300,000,000	$ 300,000,000	$ 53,000,000
Amount drawn							1,048,118,000		1,011,609,000							250,000,000		38,000,000
Additional amount with option to draw																50,000,000
Fixed rate notes							2,405,000,000	[1]	2,418,389,000	[1]		2,450,000,000	[2]	2,600,000,000	[2]			15,000,000
Fixed rate (as a percent)											5.375%							2.99%		6.19%
Repayment of unsecured notes			150,000,000	100,000,000							150,000,000
Repayments of secured mortgages						5,914,000													10,427,000
Number of operating apartment communities	247		247				8
Loss on extinguishment of debt, net	0	0	412,000	0
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 variable rate																											LIBOR	LIBOR
Debt instrument, basis spread on variable rate (as a percent)																											1.45%	2.00%	1.05%
Current interest rate (as a percent)																													1.20%
Period of borrowing rate assumed																					1 month
Annual facility fee																					1,950,000
Variable rate unsecured credit facility	0		0		0																0	0
Outstanding balance of letters of credit																					52,347,000	65,018,000
Net carrying value of apartment communities and improved land parcels securing debt																					4,440,175,000
Mortgage notes payable held by wholly owned subsidiaries guaranteed by the Company							$ 257,970,000
Weighted average interest rate, debt (as a percent)																							4.50%	4.50%	1.80%	1.80%

[1] Balances at September 30, 2014 and December 31, 2013 exclude $93,351 and $120,684 of debt premium, respectively, as reflected in mortgage notes payable on the Company’s Condensed Consolidated Balance Sheets.

[2] Balances at September 30, 2014 and December 31, 2013 exclude $4,701 and $5,291 of debt discount, respectively, as reflected in unsecured notes, net on the Company’s Condensed Consolidated Balance Sheets.