Mortgage Notes Payable, Unsecured Notes and Credit Facility (Details 2) - USD ($)	1 Months Ended		6 Months Ended
	May 31, 2019	Apr. 30, 2019	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018
Notes Payable, Unsecured Notes and Credit Facility
Cash in escrow			$ 86,468,000	$ 126,205,000	$ 248,332,000
Net carrying value of apartment communities and improved land parcels securing debt			1,667,725,000
Unsecured Notes 3.30 Percent [Domain]
Notes Payable, Unsecured Notes and Credit Facility
Debt Instrument, Face Amount			450,000,000
Proceeds from Issuance of Debt	$ 446,877,000
Variable Rate Unsecured Term Loan $250 Million [Member] | Unsecured notes
Notes Payable, Unsecured Notes and Credit Facility
Debt Instrument, Face Amount			250,000,000
Variable Rate Unsecured Term Loan $100 Million | Unsecured notes
Notes Payable, Unsecured Notes and Credit Facility
Debt Instrument, Face Amount			$ 100,000,000
Variable Rate Unsecured Term Loan $100 Million | LIBOR | Unsecured notes
Notes Payable, Unsecured Notes and Credit Facility
Debt instrument, basis spread on variable rate (as a percent)			0.90%
Variable Rate Unsecured Term Loan $150 Million | Unsecured notes
Notes Payable, Unsecured Notes and Credit Facility
Debt Instrument, Face Amount			$ 150,000,000
Variable Rate Unsecured Term Loan $150 Million | LIBOR | Unsecured notes
Notes Payable, Unsecured Notes and Credit Facility
Debt instrument, basis spread on variable rate (as a percent)			0.85%
Notes Payable Maturities 2019, Fixed Rate [Member] | Secured Debt [Member]
Notes Payable, Unsecured Notes and Credit Facility
Repayments of Secured Debt		$ 13,363,000
Notes Payable Maturities 2019, Variable Rate [Member] | Secured Debt [Member]
Notes Payable, Unsecured Notes and Credit Facility
Repayments of Secured Debt		$ 33,854,000
Unsecured Notes 3.30 Percent [Domain] | Unsecured notes
Notes Payable, Unsecured Notes and Credit Facility
Debt Instrument, Interest Rate, Stated Percentage			3.30%
Current interest rate (as a percent)			3.66%
Line of Credit [Member]
Notes Payable, Unsecured Notes and Credit Facility
Available borrowing capacity			$ 1,750,000,000	1,500,000,000
Percent of Credit Facility Available to Competitive Bid Option			65.00%
Annual facility fee, percentage			0.125%
Annual facility fee			$ 2,188,000
Outstanding balance of letters of credit			$ 35,461,000	$ 39,810,000
Line of Credit [Member] | LIBOR
Notes Payable, Unsecured Notes and Credit Facility
Debt instrument, basis spread on variable rate (as a percent)			0.775%
Current interest rate (as a percent)			3.15%
Other Letter of Credit [Member]
Notes Payable, Unsecured Notes and Credit Facility
Outstanding balance of letters of credit			$ 100,000
Fixed Rate Mortgage Notes Payable [Member]
Notes Payable, Unsecured Notes and Credit Facility
Weighted average interest rate, debt (as a percent)			3.80%	3.80%
Variable Rate Mortgage Notes Payable Unsecured Term Loan and Credit Facility [Member]
Notes Payable, Unsecured Notes and Credit Facility
Weighted average interest rate, debt (as a percent)			3.50%	3.40%
Minimum | Variable Rate Unsecured Term Loan $150 Million | LIBOR | Unsecured notes
Notes Payable, Unsecured Notes and Credit Facility
Debt instrument, basis spread on variable rate (as a percent)			0.85%
Minimum | Line of Credit [Member] | LIBOR
Notes Payable, Unsecured Notes and Credit Facility
Debt instrument, basis spread on variable rate (as a percent)			0.70%
Maximum | Variable Rate Unsecured Term Loan $150 Million | LIBOR | Unsecured notes
Notes Payable, Unsecured Notes and Credit Facility
Debt instrument, basis spread on variable rate (as a percent)			1.50%
Maximum | Line of Credit [Member] | LIBOR
Notes Payable, Unsecured Notes and Credit Facility
Debt instrument, basis spread on variable rate (as a percent)			1.45%
Eaves Mission Viejo [Member]
Notes Payable, Unsecured Notes and Credit Facility
Cash in escrow			$ 3,706,000
Eaves Mission Viejo [Member] | Notes Payable Maturities 2025 | Secured Debt [Member]
Notes Payable, Unsecured Notes and Credit Facility
Repayments of Secured Debt	7,635,000
AVA Nob Hill [Member]
Notes Payable, Unsecured Notes and Credit Facility
Cash in escrow			10,584,000
AVA Nob Hill [Member] | Notes Payable Maturities 2025 | Secured Debt [Member]
Notes Payable, Unsecured Notes and Credit Facility
Repayments of Secured Debt	20,800,000
Avalon Campbell [Member]
Notes Payable, Unsecured Notes and Credit Facility
Cash in escrow			22,622,000
Avalon Campbell [Member] | Notes Payable Maturities 2025 | Secured Debt [Member]
Notes Payable, Unsecured Notes and Credit Facility
Repayments of Secured Debt	38,800,000
Eaves Pacifica [Member]
Notes Payable, Unsecured Notes and Credit Facility
Cash in escrow			$ 10,263,000
Eaves Pacifica [Member] | Notes Payable Maturities 2025 | Secured Debt [Member]
Notes Payable, Unsecured Notes and Credit Facility
Repayments of Secured Debt	$ 17,600,000