Mortgage Notes Payable, Unsecured Notes and Credit Facility (Details 2)	1 Months Ended			3 Months Ended		9 Months Ended
	Jun. 30, 2017 USD ($)	May 31, 2017 USD ($) community	Feb. 28, 2017 USD ($)	Sep. 30, 2017 USD ($) community	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) community	Sep. 30, 2016 USD ($)	Apr. 30, 2017 USD ($)	Dec. 31, 2016 USD ($)
Notes Payable, Unsecured Notes and Credit Facility
Number of operating apartment communities | community				263		263
Loss on extinguishment of debt, net				$ 0	$ 0	$ 24,162,000	$ 2,461,000
Credit Facility				242,000,000		242,000,000			$ 0
Net carrying value of apartment communities and improved land parcels securing debt				2,204,341,000		2,204,341,000
Unsecured Notes 4.15 Percent
Notes Payable, Unsecured Notes and Credit Facility
Debt instrument, face amount				300,000,000		300,000,000
Proceeds from issuance of debt	$ 297,372,000
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 3.35 Percent
Notes Payable, Unsecured Notes and Credit Facility
Debt instrument, face amount		$ 400,000,000
Proceeds from issuance of debt		396,016,000
Notes Payable Maturities 2017 | Mortgage notes payable
Notes Payable, Unsecured Notes and Credit Facility
Repayments of secured mortgages		$ 670,590,000	$ 17,300,000
Number of operating apartment communities | community		11
Stated interest rate of unsecured notes (as a percent)		6.256%
Loss on extinguishment of debt, net		$ (10,839,000)
Variable Rate Unsecured Term Loan $250 Million
Notes Payable, Unsecured Notes and Credit Facility
Debt instrument, face amount								$ 250,000,000
Variable Rate Unsecured Term Loan $100 Million
Notes Payable, Unsecured Notes and Credit Facility
Debt instrument, face amount			100,000,000
Variable Rate Unsecured Term Loan $100 Million | LIBOR
Notes Payable, Unsecured Notes and Credit Facility
Debt instrument variable rate				LIBOR
Debt instrument, basis spread on variable rate (as a percent)				0.90%
Variable Rate Unsecured Term Loan $100 Million | LIBOR | Unsecured notes
Notes Payable, Unsecured Notes and Credit Facility
Debt instrument variable rate						LIBOR
Debt instrument, basis spread on variable rate (as a percent)						0.90%
Variable Rate Unsecured Term Loan $150 Million
Notes Payable, Unsecured Notes and Credit Facility
Debt instrument, face amount			$ 150,000,000
Variable Rate Unsecured Term Loan $150 Million | LIBOR
Notes Payable, Unsecured Notes and Credit Facility
Debt instrument variable rate				LIBOR
Debt instrument, basis spread on variable rate (as a percent)				1.50%
Variable Rate Unsecured Term Loan $150 Million | LIBOR | Unsecured notes
Notes Payable, Unsecured Notes and Credit Facility
Debt instrument variable rate						LIBOR
Debt instrument, basis spread on variable rate (as a percent)						1.50%
Notes Payable Maturities 2027 | Unsecured notes
Notes Payable, Unsecured Notes and Credit Facility
Stated interest rate of unsecured notes (as a percent)				3.35%		3.35%
Notes Payable Maturities 2027 | Mortgage notes payable
Notes Payable, Unsecured Notes and Credit Facility
Debt instrument, face amount		$ 185,100,000
Number of operating apartment communities | community		3
Stated interest rate of unsecured notes (as a percent)		3.61%
Notes Payable 3.350 Maturities 2027 | Unsecured notes
Notes Payable, Unsecured Notes and Credit Facility
Stated interest rate of unsecured notes (as a percent)		3.35%
Unsecured Notes 4.15 Percent | Unsecured notes
Notes Payable, Unsecured Notes and Credit Facility
Stated interest rate of unsecured notes (as a percent)				4.15%		4.15%
Notes Payable Maturities 2019 | Mortgage notes payable
Notes Payable, Unsecured Notes and Credit Facility
Repayments of secured mortgages	556,313,000
Number of operating apartment communities | community				12		12
Stated interest rate of unsecured notes (as a percent)				5.86%		5.86%
Loss on extinguishment of debt, net	34,965,000
Prepayment penalty	(33,515,000)
Write off of deferred debt issuance cost	$ (1,450,000)
Variable rate unsecured credit facility
Notes Payable, Unsecured Notes and Credit Facility
Available borrowing capacity				$ 1,500,000,000		$ 1,500,000,000
Line of credit facility, extension period						9 months
Extension fee						$ 1,500,000
Period of borrowing rate assumed						1 month
Annual facility fee, percentage						0.125%
Annual facility fee						$ 1,875,000
Credit Facility				242,000,000		242,000,000			0
Outstanding balance of letters of credit				$ 44,282,000		$ 44,282,000			$ 46,711,000
Variable rate unsecured credit facility | LIBOR
Notes Payable, Unsecured Notes and Credit Facility
Debt instrument variable rate						LIBOR
Debt instrument, basis spread on variable rate (as a percent)						0.825%
Current interest rate (as a percent)				2.06%		2.06%
Fixed rate mortgage notes payable
Notes Payable, Unsecured Notes and Credit Facility
Weighted average interest rate, debt (as a percent)				4.00%		4.00%			4.40%
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)				2.60%		2.60%			2.30%