Debt - Summary of Consolidated Indebtedness (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Long-term debt, gross	$ 1,770,054	$ 1,717,928
Net unamortized debt issuance costs	(6,763)	(10,383)
Unamortized fair market value of assumed debt	548	651
Mortgage and other notes payable, net	1,125,356	1,170,076
Unsecured notes payable, net	500,083	477,320
Total Indebtedness	1,763,839	1,708,196
Mortgages
Debt Instrument [Line Items]
Net unamortized debt issuance costs	(6,507)	(10,078)
Unamortized fair market value of assumed debt	548	651
Mortgage and other notes payable, net	1,125,356	$ 1,170,076
Mortgages | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate		1.70%
Unsecured Debt
Debt Instrument [Line Items]
Net unamortized debt issuance costs	(256)	$ (305)
Unsecured notes payable, net	$ 500,083	477,320
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	1.25%
Core Portfolio | Mortgages
Debt Instrument [Line Items]
Long-term debt, gross	$ 228,310	257,735
Core Portfolio | Mortgages | Fixed Rate
Debt Instrument [Line Items]
Long-term debt, gross	$ 147,810	$ 176,176
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%	6.00%
Maturity Date	2035-04
Core Portfolio | Mortgages | Variable Rate - Swapped
Debt Instrument [Line Items]
Long-term debt, gross	$ 80,500	$ 81,559
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	$ 380,000	$ 350,000
Core Portfolio | Unsecured Debt | Variable Rate Unsecured Term Loans - Swapped
Debt Instrument [Line Items]
Maturity Date	2023-03
Long-term debt, gross	$ 350,000	$ 350,000
Core Portfolio | Unsecured Debt | Variable Rate Unsecured Term Loans - Swapped | Minimum
Debt Instrument [Line Items]
Interest rate, stated percentage	2.49%	2.49%
Core Portfolio | Unsecured Debt | Variable Rate Unsecured Term Loans - Swapped | Maximum
Debt Instrument [Line Items]
Interest rate, stated percentage	5.02%	5.02%
Core Portfolio | Unsecured Debt | Variable Rate Unsecured Term Loans - Swapped | LIBOR
Debt Instrument [Line Items]
Interest rate, stated percentage	2.55%
Maturity Date	2021-06
Core Portfolio | Unsecured Debt | Unsecured Line of Credit - Swapped
Debt Instrument [Line Items]
Maturity Date	2022-03
Core Portfolio | Unsecured Debt | Variable Rate Unsecured Term Loans
Debt Instrument [Line Items]
Long-term debt, gross	$ 30,000
Core Portfolio | Line of Credit | Unsecured Line of Credit - Swapped
Debt Instrument [Line Items]
Long-term debt, gross	$ 138,400	$ 60,800
Core Portfolio | Line of Credit | Unsecured Line of Credit - Swapped | Minimum
Debt Instrument [Line Items]
Interest rate, stated percentage	2.49%	2.49%
Core Portfolio | Line of Credit | Unsecured Line of Credit - Swapped | Maximum
Debt Instrument [Line Items]
Interest rate, stated percentage	5.02%	5.02%
Fixed Rate
Debt Instrument [Line Items]
Long-term debt, gross	$ 1,143,152	$ 1,403,324
Variable Rate
Debt Instrument [Line Items]
Long-term debt, gross	626,902	314,604
Fund II | Fund Portfolio
Debt Instrument [Line Items]
Long-term debt, gross	$ 228,282	24,225
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	$ 247,085	$ 243,298
Fund II | Fund Portfolio | Mortgages | Fixed Rate
Debt Instrument [Line Items]
Interest rate, stated percentage		4.75%
Long-term debt, gross		$ 200,000
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	$ 18,803	$ 19,073
Fund II | Fund Portfolio | Mortgages | Variable Rate Debt | Minimum
Debt Instrument [Line Items]
Maturity Date	2022-03
Fund II | Fund Portfolio | Mortgages | Variable Rate Debt | Maximum
Debt Instrument [Line Items]
Maturity Date	2022-05
Fund II | Fund Portfolio | Mortgages | Variable Rate Debt | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate	3.00%	3.00%
Fund II | Fund Portfolio | Mortgages | Variable Rate Debt | Prime Rate
Debt Instrument [Line Items]
Basis spread on variable rate	2.00%
Fund II | Fund Portfolio | Unsecured Debt | Variable Rate Debt | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate	1.65%	1.65%
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]
Maturity Date	2021-09
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	$ 71,918	$ 74,554
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	2021-06
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	2.25%
Fund IV | Fund Portfolio | Mortgages
Debt Instrument [Line Items]
Long-term debt, gross	$ 248,325	$ 267,903
Fund IV | Fund Portfolio | Mortgages | Fixed Rate
Debt Instrument [Line Items]
Long-term debt, gross	$ 6,726	$ 8,189
Fund IV | Fund Portfolio | Mortgages | Fixed Rate | Minimum
Debt Instrument [Line Items]
Interest rate, stated percentage	3.40%	3.40%
Maturity Date	2025-10
Fund IV | Fund Portfolio | Mortgages | Fixed Rate | Maximum
Debt Instrument [Line Items]
Interest rate, stated percentage	4.50%	4.50%
Maturity Date	2026-06
Fund IV | Fund Portfolio | Mortgages | Variable Rate - Swapped
Debt Instrument [Line Items]
Long-term debt, gross	$ 66,590	$ 102,699
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	$ 175,009	$ 157,015
Fund IV | Fund Portfolio | Mortgages | Variable Rate Debt | LIBOR | Minimum
Debt Instrument [Line Items]
Basis spread on variable rate	1.60%	1.60%
Maturity Date	2021-02
Fund IV | Fund Portfolio | Mortgages | Variable Rate Debt | LIBOR | Maximum
Debt Instrument [Line Items]
Basis spread on variable rate	3.40%	3.40%
Maturity Date	2025-10
Fund IV | Fund Portfolio | Unsecured Debt | Term Loan / Subscription Facility
Debt Instrument [Line Items]
Long-term debt, gross	$ 80,089	$ 87,625
Fund IV | Fund Portfolio | Unsecured Debt | Term Loan / Subscription Facility | LIBOR | Minimum
Debt Instrument [Line Items]
Basis spread on variable rate	1.90%	1.65%
Maturity Date	2021-06
Fund IV | Fund Portfolio | Unsecured Debt | Term Loan / Subscription Facility | LIBOR | Maximum
Debt Instrument [Line Items]
Basis spread on variable rate	2.00%	2.00%
Maturity Date	2021-12
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	$ 335,677	$ 336,013
Fund V | Fund Portfolio | Mortgages | Variable Rate - Swapped
Debt Instrument [Line Items]
Long-term debt, gross	$ 334,323	$ 334,626
Fund V | Fund Portfolio | Mortgages | Variable Rate - Swapped | Minimum
Debt Instrument [Line Items]
Basis spread on variable rate	2.95%	2.95%
Maturity Date	2021-02
Fund V | Fund Portfolio | Mortgages | Variable Rate - Swapped | Maximum
Debt Instrument [Line Items]
Basis spread on variable rate	4.78%	4.78%
Maturity Date	2024-12
Fund V | Fund Portfolio | Mortgages | Variable Rate Debt
Debt Instrument [Line Items]
Long-term debt, gross	$ 1,354	$ 1,387
Fund V | Fund Portfolio | Mortgages | Variable Rate Debt | LIBOR | Minimum
Debt Instrument [Line Items]
Basis spread on variable rate	1.50%	1.50%
Maturity Date	2021-02
Fund V | Fund Portfolio | Mortgages | Variable Rate Debt | LIBOR | Maximum
Debt Instrument [Line Items]
Basis spread on variable rate	2.20%	2.20%
Maturity Date	2024-12
Fund V | Fund Portfolio | Unsecured Debt | Subscription Line
Debt Instrument [Line Items]
Long-term debt, gross	$ 250	$ 0
Fund V | Fund Portfolio | Unsecured Debt | Subscription Line | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate	1.60%
Maturity Date	2021-05