Notes Payable, Unsecured Notes and Credit Facility (Details 2)		1 Months Ended	3 Months Ended	12 Months Ended
		Feb. 29, 2016 USD ($)	Mar. 31, 2016 USD ($) community	Dec. 31, 2015 USD ($)	Jan. 31, 2016 USD ($)
Notes Payable, Unsecured Notes and Credit Facility
Number of operating apartment communities | community			258
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			$ 234,500,000
Notes Payable Maturities 2016 [Member] | Mortgage notes payable
Notes Payable, Unsecured Notes and Credit Facility
Repayments of secured mortgages		$ 16,212,000
Current interest rate (as a percent)		3.32%
Notes Payable Maturities 2016 [Member] | Unsecured notes
Notes Payable, Unsecured Notes and Credit Facility
Debt Instrument, Interest Rate, Stated Percentage			5.75%
Variable rate unsecured credit facility
Notes Payable, Unsecured Notes and Credit Facility
Available borrowing capacity			$ 1,500,000,000	1,300,000,000
Line of credit facility, extension period			9 months
Extension fee			$ 1,500,000
Period of borrowing rate assumed			1 month
Annual facility fee			$ 1,875,000
Outstanding balance of letters of credit			51,233,000	43,049,000
Variable rate unsecured credit facility			0	$ 0
Net carrying value of apartment communities and improved land parcels securing debt			$ 3,364,440,000
Percent of Credit Facility Available to Competitive Bid Option			65.00%
Line of Credit Facility, Commitment Fee Percentage			0.125%	0.15%
Fixed rate mortgage notes payable
Notes Payable, Unsecured Notes and Credit Facility
Weighted average interest rate, debt (as a percent)			4.50%	4.60%
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)			1.90%	1.80%
LIBOR | Variable Rate Unsecured Term Loan [Member] | 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
Current interest rate (as a percent)			1.26%
Debt instrument, basis spread on variable rate (as a percent)			0.825%
Minimum [Member] | Variable rate unsecured credit facility
Notes Payable, Unsecured Notes and Credit Facility
Debt instrument, basis spread on variable rate (as a percent)			0.80%
Maximum [Member] | Variable rate unsecured credit facility
Notes Payable, Unsecured Notes and Credit Facility
Debt instrument, basis spread on variable rate (as a percent)			1.55%
Avalon Hoboken [Member] | Notes Payable Maturities 2020 [Member] | Mortgage notes payable
Notes Payable, Unsecured Notes and Credit Facility
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Long-term Debt	[1]				$ 67,904,000
Current interest rate (as a percent)					4.18%

[1] Balances at March 31, 2016 and December 31, 2015 exclude $16,652 and $19,686, respectively, of debt premium, and $14,760 and $14,703, respectively, of deferred financing costs, as reflected in mortgage notes payable on the Company’s Condensed Consolidated Balance Sheets.