Mortgage Notes Payable, Unsecured Notes and Credit Facility (Details 2) - USD ($)	1 Months Ended			3 Months Ended		6 Months Ended		12 Months Ended
	May 31, 2016	Apr. 30, 2016	Feb. 29, 2016	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015	Jan. 31, 2016
Notes Payable, Unsecured Notes and Credit Facility
Current interest rate (as a percent)	3.35%
Loss (gain) on extinguishment of debt, net				$ 2,461,000	$ (7,749,000)	$ 2,461,000	$ (7,749,000)
Debt Instrument, Interest Rate, Stated Percentage	2.95%
Variable rate unsecured credit facility				0		0		$ 0
Mortgage notes payable
Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable held by wholly owned subsidiaries guaranteed by the Company				$ 100,000,000		$ 100,000,000
Unsecured Notes 2.95 Percent [Member]
Notes Payable, Unsecured Notes and Credit Facility
Debt Instrument, Face Amount	$ 475,000,000
Proceeds from Issuance of Debt	$ 471,751,000
Notes Payable Maturities 2020 [Member] | Avalon Hoboken [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									$ 67,904,000
Current interest rate (as a percent)									4.18%
Notes Payable Maturities 2016 [Member] | Unsecured notes
Notes Payable, Unsecured Notes and Credit Facility
Debt Instrument, Interest Rate, Stated Percentage				5.75%		5.75%
Notes Payable Maturities 2016 [Member] | Mortgage notes payable
Notes Payable, Unsecured Notes and Credit Facility
Current interest rate (as a percent)			3.32%
Repayments of secured mortgages			$ 16,212,000
Notes Payable Maturities 2046 [Member]
Notes Payable, Unsecured Notes and Credit Facility
Loss (gain) on extinguishment of debt, net		$ (2,461,000)
Notes Payable Maturities 2046 [Member] | Mortgage notes payable
Notes Payable, Unsecured Notes and Credit Facility
Repayments of secured mortgages		$ 134,500,000
Secured Mortgage | LIBOR
Notes Payable, Unsecured Notes and Credit Facility
Debt instrument variable rate						LIBOR
Variable rate unsecured credit facility
Notes Payable, Unsecured Notes and Credit Facility
Available borrowing capacity				$ 1,500,000,000		$ 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
Percent of Credit Facility Available to Competitive Bid Option				65.00%		65.00%
Line of Credit Facility, Commitment Fee Percentage						0.125%		0.15%
Annual facility fee						$ 1,875,000
Variable rate unsecured credit facility				$ 0		0		$ 0
Outstanding balance of letters of credit				50,620,000		50,620,000		$ 43,049,000
Net carrying value of apartment communities and improved land parcels securing debt				$ 3,346,769,000		$ 3,346,769,000
Variable rate unsecured credit facility | LIBOR
Notes Payable, Unsecured Notes and Credit Facility
Current interest rate (as a percent)				1.29%		1.29%
Debt instrument, basis spread on variable rate (as a percent)						0.825%
Variable rate unsecured credit facility | Minimum [Member]
Notes Payable, Unsecured Notes and Credit Facility
Debt instrument, basis spread on variable rate (as a percent)						0.80%
Variable rate unsecured credit facility | Maximum [Member]
Notes Payable, Unsecured Notes and Credit Facility
Debt instrument, basis spread on variable rate (as a percent)						1.55%
Fixed rate mortgage notes payable
Notes Payable, Unsecured Notes and Credit Facility
Weighted average interest rate, debt (as a percent)				4.50%		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)				2.10%		2.10%		1.80%