Indebtedness Mortgage debt summary by segment (Details) - USD ($)	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Secured Debt	$ 2,609,829,000
Long-term Debt, Weighted Average Interest Rate, at Point in Time	4.04%
average maturity mortgage debt	9 years 1 month
Deferred Finance Costs, Own-share Lending Arrangement, Issuance Costs, Accumulated Amortization Adjustment	$ (38,185,000)
Mark-to-Market debt	(4,622,000)
Long-term Debt	2,567,022,000	$ 2,299,625,000
Fixed Income Interest Rate [Member]
Debt Instrument [Line Items]
Secured Debt	$ 2,433,442,000
Long-term Debt, Weighted Average Interest Rate, at Point in Time	4.00%
average maturity mortgage debt	9 years 7 months
Variable Income Interest Rate [Member]
Debt Instrument [Line Items]
Secured Debt	$ 176,387,000
Long-term Debt, Weighted Average Interest Rate, at Point in Time	4.57%
average maturity mortgage debt	2 years 6 months
Multifamily Communities
Debt Instrument [Line Items]
Secured Debt	$ 1,173,901,000
Long-term Debt, Weighted Average Interest Rate, at Point in Time	3.87%
average maturity mortgage debt	8 years 11 months
Multifamily Communities \| Fixed Income Interest Rate [Member]
Debt Instrument [Line Items]
Secured Debt	$ 1,135,030,000
Long-term Debt, Weighted Average Interest Rate, at Point in Time	3.89%
average maturity mortgage debt	9 years 1 month
Multifamily Communities \| Variable Income Interest Rate [Member]
Debt Instrument [Line Items]
Secured Debt	$ 38,871,000
Long-term Debt, Weighted Average Interest Rate, at Point in Time	3.38%
average maturity mortgage debt	4 years 7 months
Retail Segment [Member]
Debt Instrument [Line Items]
Secured Debt	$ 621,090,000
Long-term Debt, Weighted Average Interest Rate, at Point in Time	3.98%
average maturity mortgage debt	7 years 9 months
Retail Segment [Member] \| Fixed Income Interest Rate [Member]
Debt Instrument [Line Items]
Secured Debt	$ 573,940,000
Long-term Debt, Weighted Average Interest Rate, at Point in Time	3.95%
average maturity mortgage debt	8 years 1 month
Retail Segment [Member] \| Variable Income Interest Rate [Member]
Debt Instrument [Line Items]
Secured Debt	$ 47,150,000
Long-term Debt, Weighted Average Interest Rate, at Point in Time	4.32%
average maturity mortgage debt	3 years 10 months
Office Building [Member]
Debt Instrument [Line Items]
Secured Debt	$ 565,254,000
Long-term Debt, Weighted Average Interest Rate, at Point in Time	4.22%
average maturity mortgage debt	13 years 6 months
Office Building [Member] \| Fixed Income Interest Rate [Member]
Debt Instrument [Line Items]
Secured Debt	$ 565,254,000
Long-term Debt, Weighted Average Interest Rate, at Point in Time	4.22%
average maturity mortgage debt	13 years 6 months
Office Building [Member] \| Variable Income Interest Rate [Member]
Debt Instrument [Line Items]
Secured Debt	$ 0
Long-term Debt, Weighted Average Interest Rate, at Point in Time	0.00%
Student Housing Communities [Member]
Debt Instrument [Line Items]
Secured Debt	$ 249,584,000
Long-term Debt, Weighted Average Interest Rate, at Point in Time	4.52%
average maturity mortgage debt	3 years 11 months
Student Housing Communities [Member] \| Fixed Income Interest Rate [Member]
Debt Instrument [Line Items]
Secured Debt	$ 159,218,000
Long-term Debt, Weighted Average Interest Rate, at Point in Time	4.13%
average maturity mortgage debt	5 years 7 months
Student Housing Communities [Member] \| Variable Income Interest Rate [Member]
Debt Instrument [Line Items]
Secured Debt	$ 90,366,000
Long-term Debt, Weighted Average Interest Rate, at Point in Time	5.21%
average maturity mortgage debt	1 year

average maturity mortgage debt

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- Definition

Mark-to-Market debt

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No definition available.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

Amount of increase (decrease) in accumulated amortization of deferred issuance costs associated with a share-lending arrangement.

+ References

No definition available.

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- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition

Weighted average interest rate of long-term debt outstanding calculated at point in time.

+ References

No definition available.

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- Definition

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.

+ References

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