Mortgage Notes Payable (Details)	12 Months Ended
Dec. 31, 2018 USD ($) property	Dec. 31, 2017 USD ($) property
Debt Instrument [Line Items]
Mortgage notes payable	$ 1,806,626,000	$ 2,008,417,000
Number of properties securing mortgage notes \| property	50	56
Weighted average interest rate (in hundredths)	4.30%	4.20%
Unamortized debt issuance expense	$ 4,200,000	$ 5,400,000
Monthly interest expense	7,600,000
Monthly principal amortization	2,300,000
Mortgage notes payable, net	$ 1,806,626,000	$ 2,008,417,000
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 principal being prepaid multiplied by the difference between the interest rate of the mortgage note and the stated yield rate on a U.S. treasury security which generally has an equivalent remaining term as the mortgage note.
Minimum [Member]
Debt Instrument [Line Items]
Remaining terms	1 year	1 year
Maximum [Member]
Debt Instrument [Line Items]
Remaining terms	28 years	29 years
Fixed rate mortgage notes payable [Member]
Debt Instrument [Line Items]
Mortgage notes payable	$ 1,538,488,000	$ 1,739,856,000
Prepayment penalty, percent of principal prepaid	1.00%
Variable rate mortgage notes payable [Member]
Debt Instrument [Line Items]
Mortgage notes payable	$ 268,138,000	$ 268,561,000
Bond subject to interest rate caps	$ 256,000,000
Multifamily housing mortgage revenue bonds, variable interest rate (in hundredths)	2.50%	2.00%
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	$ 9,900,000
Secured Debt [Member]
Debt Instrument [Line Items]
Mortgage notes payable	1,795,895,000
Debt instrument, unamortized premium	14,900,000	$ 33,200,000
Secured Deeds of Trust [Member]
Debt Instrument [Line Items]
Mortgage notes payable, net	$ 0	$ 0

The Bonds that are subject to interest rate cap agreements.

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Represents payment remaining terms of the debt instrument (for example, whether periodic payments include principal and frequency of payments) and discussion about any contingencies associated with the payment in "PnYnMnD" format.

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Debt Instrument, Prepayment Penalty, Percent Of Principal Prepaid

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The mortgage interest expense on a monthly basis.

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The monthly amount of principal payable on mortgage loans on real estate.

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The possible penalties for the repayment of debt before scheduled maturity date.

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Refers to number of properties securing mortgage notes.

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The percentage of units subject to tenant income criteria under the multifamily housing mortgage bonds loan agreement.

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Amount, after accumulated amortization, of debt premium.

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Weighted average interest rate of debt outstanding.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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The interest rate applicable to the portion of the carrying amount of long-term borrowings outstanding as of the balance sheet date, including current maturities, which accrues interest at a rate subject to change from time to time.

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Carrying value as of the balance sheet date, including the current and noncurrent portions, of collateralized debt obligations (with maturities initially due after one year or beyond the operating cycle, if longer). Such obligations include mortgage loans, chattel loans, and any other borrowings secured by assets of the borrower.

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The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of the respective bond issues. This does not include the amounts capitalized as part of the cost of the utility plant or asset.

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