Mortgage Notes Payable (Details)	12 Months Ended
	Dec. 31, 2017 USD ($) property	Dec. 31, 2016 USD ($) property
Debt Instrument [Line Items]
Mortgage notes payable	$ 2,008,417,000	$ 2,191,481,000
Number of properties securing mortgage notes | property	56	61
Weighted average interest rate (in hundredths)	4.20%	4.30%
Unamortized debt issuance expense	$ 5,400,000	$ 7,400,000
Monthly interest expense	7,000,000
Monthly principal amortization	2,500,000
Mortgage notes payable, net	$ 2,008,417,000	$ 2,191,481,000
Repayment of debt before the scheduled maturity date, prepayment penalties	The prepayment penalty on the majority of the Company’s mortgage notes payable are computed by the greater of (a) 1% of the amount of the principal being prepaid or (b) the present value of the mortgage note payable which is calculated by multiplying the principal being prepaid by the difference between the interest rate of the mortgage note and the stated yield rate on a specified U.S. treasury security as defined in the mortgage note agreement.
Minimum [Member]
Debt Instrument [Line Items]
Remaining terms	1 year	1 year
Maximum [Member]
Debt Instrument [Line Items]
Remaining terms	29 years	30 years
Fixed rate mortgage notes payable [Member]
Debt Instrument [Line Items]
Mortgage notes payable	$ 1,739,856,000	$ 1,911,699,000
Prepayment penalty, percent of principal prepaid	1.00%
Variable rate mortgage notes payable [Member]
Debt Instrument [Line Items]
Mortgage notes payable	$ 268,561,000	$ 279,782,000
Bond subject to interest rate caps	$ 256,600,000
Multifamily housing mortgage revenue bonds, variable interest rate (in hundredths)	2.00%	1.20%
Percentage of units subject to tenant income criteria (in hundredths)	20.00%
Variable rate mortgage notes payable [Member] | Total Return Swap [Member]
Debt Instrument [Line Items]
Bond subject to interest rate caps	$ 20,700,000
Secured Debt [Member]
Debt Instrument [Line Items]
Mortgage notes payable	1,980,561,000
Debt instrument, unamortized premium	33,200,000	$ 50,800,000
Secured Deeds of Trust [Member]
Debt Instrument [Line Items]
Mortgage notes payable, net	$ 0	$ 0