Debt - Summary of Consolidated Indebtedness (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
Sep. 30, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Long-term debt, gross	$ 1,796,209	$ 1,770,054
Net unamortized debt issuance costs	(8,781)	(6,763)
Unamortized premium	471	548
Mortgage and other notes payable, net	1,181,028	1,204,581
Unsecured notes payable, net	503,966	420,858
Total Indebtedness	1,787,899	1,763,839
Fixed Rate
Debt Instrument [Line Items]
Long-term debt, gross	1,114,038	1,143,152
Mortgages
Debt Instrument [Line Items]
Net unamortized debt issuance costs	(4,671)	(6,507)
Unamortized premium	471	548
Mortgage and other notes payable, net	1,181,028	1,204,581
Unsecured Debt
Debt Instrument [Line Items]
Net unamortized debt issuance costs	(4,110)	(256)
Unsecured notes payable, net	$ 503,966	420,858
Core Portfolio \| Variable Rate Debt \| LIBOR \| Minimum
Debt Instrument [Line Items]
Basis spread on variable rate	1.50%
Core Portfolio \| Variable Rate Debt \| LIBOR \| Maximum
Debt Instrument [Line Items]
Basis spread on variable rate	1.90%
Core Portfolio \| Unsecured Notes Payable \| LIBOR \| Minimum
Debt Instrument [Line Items]
Basis spread on variable rate	1.55%
Core Portfolio \| Mortgages
Debt Instrument [Line Items]
Long-term debt, gross	$ 219,225	228,310
Core Portfolio \| Mortgages \| Fixed Rate
Debt Instrument [Line Items]
Long-term debt, gross	$ 146,061	$ 147,810
Core Portfolio \| Mortgages \| Fixed Rate \| Minimum
Debt Instrument [Line Items]
Interest rate, stated percentage	3.88%	3.88%
Maturity Date	2024-02
Core Portfolio \| Mortgages \| Fixed Rate \| Maximum
Debt Instrument [Line Items]
Interest rate, stated percentage	5.89%	5.89%
Maturity Date	2035-04
Core Portfolio \| Mortgages \| Variable Rate - Swapped
Debt Instrument [Line Items]
Long-term debt, gross	$ 73,164	$ 80,500
Core Portfolio \| Mortgages \| Variable Rate - Swapped \| Minimum
Debt Instrument [Line Items]
Interest rate, stated percentage	3.41%	3.41%
Maturity Date	2023-01
Core Portfolio \| Mortgages \| Variable Rate - Swapped \| Maximum
Debt Instrument [Line Items]
Interest rate, stated percentage	4.54%	4.54%
Maturity Date	2028-11
Core Portfolio \| Unsecured Debt
Debt Instrument [Line Items]
Long-term debt, gross	$ 400,000	$ 380,000
Core Portfolio \| Unsecured Debt \| Variable Rate Credit Facility
Debt Instrument [Line Items]
Long-term debt, gross		$ 30,000
Core Portfolio \| Unsecured Debt \| Variable Rate Credit Facility \| LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate		2.55%
Core Portfolio \| Unsecured Debt \| Variable Rate Unsecured Term Loans - Swapped
Debt Instrument [Line Items]
Maturity Date	2026-06
Long-term debt, gross	$ 400,000	$ 350,000
Core Portfolio \| Unsecured Debt \| Variable Rate Unsecured Term Loans - Swapped \| Minimum
Debt Instrument [Line Items]
Interest rate, stated percentage	3.65%	2.49%
Core Portfolio \| Unsecured Debt \| Variable Rate Unsecured Term Loans - Swapped \| Maximum
Debt Instrument [Line Items]
Interest rate, stated percentage	5.32%	5.02%
Core Portfolio \| Line of Credit \| Unsecured Line of Credit - Swapped
Debt Instrument [Line Items]
Maturity Date	2025-06
Long-term debt, gross	$ 102,905	$ 138,400
Core Portfolio \| Line of Credit \| Unsecured Line of Credit - Swapped \| Minimum
Debt Instrument [Line Items]
Interest rate, stated percentage	3.65%	2.49%
Core Portfolio \| Line of Credit \| Unsecured Line of Credit - Swapped \| Maximum
Debt Instrument [Line Items]
Interest rate, stated percentage	5.32%	5.02%
Variable Rate
Debt Instrument [Line Items]
Long-term debt, gross	$ 682,171	$ 626,902
Fund II \| Fund Portfolio
Debt Instrument [Line Items]
Long-term debt, gross	$ 237,943	228,282
Fund II \| Fund Portfolio \| Variable Rate Debt \| LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate	1.39%
Fund II \| Fund Portfolio \| Mortgages
Debt Instrument [Line Items]
Long-term debt, gross	$ 256,531	$ 247,085
Fund II \| Fund Portfolio \| Mortgages \| Variable Rate - Swapped
Debt Instrument [Line Items]
Interest rate, stated percentage	2.88%	2.88%
Maturity Date	2021-11
Long-term debt, gross	$ 18,588	$ 18,803
Fund II \| Fund Portfolio \| Mortgages \| Variable Rate Debt \| LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate	3.00%	3.00%
Maturity Date	2022-03
Fund II \| Fund Portfolio \| Mortgages \| Variable Rate Debt \| Prime Rate
Debt Instrument [Line Items]
Basis spread on variable rate	2.00%	2.00%
Maturity Date	2022-08
Fund II \| Fund Portfolio \| Unsecured Debt \| Unsecured Notes Payable
Debt Instrument [Line Items]
Long-term debt, gross	$ 40,000	$ 40,000
Fund II \| Fund Portfolio \| Unsecured Debt \| Unsecured Notes Payable \| LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate	2.25%	1.65%
Maturity Date	2022-09
Fund III \| Fund Portfolio \| Variable Rate Debt \| LIBOR \| Minimum
Debt Instrument [Line Items]
Basis spread on variable rate	2.75%
Fund III \| Fund Portfolio \| Variable Rate Debt \| LIBOR \| Maximum
Debt Instrument [Line Items]
Basis spread on variable rate	3.10%
Fund III \| Fund Portfolio \| Mortgages \| Variable Rate Debt
Debt Instrument [Line Items]
Long-term debt, gross	$ 71,003	$ 71,918
Fund III \| Fund Portfolio \| Mortgages \| Variable Rate Debt \| LIBOR \| Minimum
Debt Instrument [Line Items]
Basis spread on variable rate	2.75%	2.75%
Maturity Date	2022-06
Fund III \| Fund Portfolio \| Mortgages \| Variable Rate Debt \| LIBOR \| Maximum
Debt Instrument [Line Items]
Basis spread on variable rate	3.10%	3.10%
Maturity Date	2022-07
Fund IV \| Fund Portfolio \| LIBOR \| Minimum
Debt Instrument [Line Items]
Basis spread on variable rate	1.75%
Fund IV \| Fund Portfolio \| LIBOR \| Maximum
Debt Instrument [Line Items]
Basis spread on variable rate	2.00%
Fund IV \| Fund Portfolio \| Mortgages
Debt Instrument [Line Items]
Long-term debt, gross	$ 278,630	$ 327,550
Fund IV \| Fund Portfolio \| Mortgages \| Fixed Rate
Debt Instrument [Line Items]
Interest rate, stated percentage	4.50%
Maturity Date	2025-10
Long-term debt, gross	$ 1,120	$ 6,726
Fund IV \| Fund Portfolio \| Mortgages \| Fixed Rate \| Minimum
Debt Instrument [Line Items]
Interest rate, stated percentage		3.40%
Fund IV \| Fund Portfolio \| Mortgages \| Fixed Rate \| Maximum
Debt Instrument [Line Items]
Interest rate, stated percentage		4.50%
Fund IV \| Fund Portfolio \| Mortgages \| Variable Rate - Swapped
Debt Instrument [Line Items]
Long-term debt, gross	$ 42,385	$ 66,590
Fund IV \| Fund Portfolio \| Mortgages \| Variable Rate - Swapped \| Minimum
Debt Instrument [Line Items]
Basis spread on variable rate	3.48%	3.48%
Maturity Date	2022-04
Fund IV \| Fund Portfolio \| Mortgages \| Variable Rate - Swapped \| Maximum
Debt Instrument [Line Items]
Basis spread on variable rate	4.61%	4.61%
Maturity Date	2022-12
Fund IV \| Fund Portfolio \| Mortgages \| Variable Rate Debt
Debt Instrument [Line Items]
Long-term debt, gross	$ 235,125	$ 254,234
Fund IV \| Fund Portfolio \| Mortgages \| Variable Rate Debt \| Minimum
Debt Instrument [Line Items]
Basis spread on variable rate	1.60%
Fund IV \| Fund Portfolio \| Mortgages \| Variable Rate Debt \| Maximum
Debt Instrument [Line Items]
Basis spread on variable rate	3.65%
Fund IV \| Fund Portfolio \| Mortgages \| Variable Rate Debt \| LIBOR \| Minimum
Debt Instrument [Line Items]
Basis spread on variable rate		1.60%
Maturity Date	2021-11
Fund IV \| Fund Portfolio \| Mortgages \| Variable Rate Debt \| LIBOR \| Maximum
Debt Instrument [Line Items]
Basis spread on variable rate		3.40%
Maturity Date	2026-06
Fund IV \| Fund Portfolio \| Unsecured Debt \| Term Loan Subscription Facility
Debt Instrument [Line Items]
Long-term debt, gross		$ 864
Fund IV \| Fund Portfolio \| Unsecured Debt \| Term Loan Subscription Facility \| LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate	1.90%	1.90%
Maturity Date	2021-12
Fund V \| Unsecured Debt \| Subscription Line
Debt Instrument [Line Items]
Maturity Date	2022-05
Fund V \| Fund Portfolio \| LIBOR \| Minimum
Debt Instrument [Line Items]
Basis spread on variable rate	1.50%
Fund V \| Fund Portfolio \| LIBOR \| Maximum
Debt Instrument [Line Items]
Basis spread on variable rate	2.20%
Fund V \| Fund Portfolio \| Mortgages
Debt Instrument [Line Items]
Long-term debt, gross	$ 359,839	$ 335,677
Fund V \| Fund Portfolio \| Mortgages \| Fixed Rate
Debt Instrument [Line Items]
Interest rate, stated percentage	3.35%
Maturity Date	2023-05
Long-term debt, gross	$ 31,801
Fund V \| Fund Portfolio \| Mortgages \| Variable Rate - Swapped
Debt Instrument [Line Items]
Long-term debt, gross	$ 298,014	$ 334,323
Fund V \| Fund Portfolio \| Mortgages \| Variable Rate - Swapped \| Minimum
Debt Instrument [Line Items]
Interest rate, stated percentage	2.43%	2.95%
Maturity Date	2022-02
Fund V \| Fund Portfolio \| Mortgages \| Variable Rate - Swapped \| Maximum
Debt Instrument [Line Items]
Interest rate, stated percentage	4.78%	4.78%
Maturity Date	2024-12
Fund V \| Fund Portfolio \| Mortgages \| Variable Rate Debt
Debt Instrument [Line Items]
Long-term debt, gross	$ 30,024
Fund V \| Fund Portfolio \| Mortgages \| Variable Rate Debt \| LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate	1.85%
Maturity Date	2022-06
Long-term debt, gross		$ 1,354
Fund V \| Fund Portfolio \| Mortgages \| Variable Rate Debt \| LIBOR \| Minimum
Debt Instrument [Line Items]
Basis spread on variable rate	1.50%
Fund V \| Fund Portfolio \| Mortgages \| Variable Rate Debt \| LIBOR \| Maximum
Debt Instrument [Line Items]
Basis spread on variable rate		2.20%
Fund V \| Fund Portfolio \| Unsecured Debt \| Subscription Line
Debt Instrument [Line Items]
Long-term debt, gross	$ 68,076	$ 250
Fund V \| Fund Portfolio \| Unsecured Debt \| Subscription Line \| LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate	1.90%	1.60%
Maturity Date	2022-05

Debt instrument, maturity month and year.

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- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

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Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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Contractual interest rate for funds borrowed, under the debt agreement.

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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.

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Amount, after accumulated amortization, of debt premium.

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Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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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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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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Including the current and noncurrent portions, carrying value as of the balance sheet date of uncollateralized debt obligations (with maturities initially due after one year or beyond the operating cycle if longer).

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