Investments in Unconsolidated Real Estate Ventures - Summary of Composition of Investments (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Schedule of Equity Method Investments [Line Items]
Total investments in unconsolidated real estate ventures	$ 486,052	$ 461,369
Difference between the investments in unconsolidated real estate ventures and the net book value of the underlying assets	$ 20,200	18,900
Prudential Global Investment Management (PGIM)
Schedule of Equity Method Investments [Line Items]
Ownership interest (as percent)	50.00%
Total investments in unconsolidated real estate ventures	$ 209,261	216,939
Landmark
Schedule of Equity Method Investments [Line Items]
Total investments in unconsolidated real estate ventures	$ 53,295	66,724
Landmark \| Minimum
Schedule of Equity Method Investments [Line Items]
Ownership interest (as percent)	1.80%
Landmark \| Maximum
Schedule of Equity Method Investments [Line Items]
Ownership interest (as percent)	49.00%
CBREI Venture
Schedule of Equity Method Investments [Line Items]
Total investments in unconsolidated real estate ventures	$ 59,028	65,190
CBREI Venture \| Minimum
Schedule of Equity Method Investments [Line Items]
Ownership interest (as percent)	5.00%
CBREI Venture \| Maximum
Schedule of Equity Method Investments [Line Items]
Ownership interest (as percent)	64.00%
Canadian Pension Plan Investment Board (CPPIB)
Schedule of Equity Method Investments [Line Items]
Ownership interest (as percent)	55.00%
Total investments in unconsolidated real estate ventures	$ 49,098	47,522
J.P. Morgan Global Alternatives ("J.P. Morgan")
Schedule of Equity Method Investments [Line Items]
Ownership interest (as percent)	50.00%
Total investments in unconsolidated real estate ventures	$ 47,362
Berkshire Group
Schedule of Equity Method Investments [Line Items]
Ownership interest (as percent)	50.00%
Total investments in unconsolidated real estate ventures	$ 53,589	50,649
Brandywine Realty Trust
Schedule of Equity Method Investments [Line Items]
Ownership interest (as percent)	30.00%
Total investments in unconsolidated real estate ventures	$ 13,755	13,710
Other
Schedule of Equity Method Investments [Line Items]
Total investments in unconsolidated real estate ventures	664	635
1101 17th Street \| Canadian Pension Plan Investment Board (CPPIB)
Schedule of Equity Method Investments [Line Items]
Total investments in unconsolidated real estate ventures	$ 0	$ 0

Difference between amount at which an investment accounted for under the equity method of accounting is carried (reported) on the balance sheet and amount of underlying equity in net assets the reporting Entity has in the investee.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)(3)
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The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=114001798&loc=d3e33918-111571

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+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.1(d))
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

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