Overview - Schedule of Properties Portfolio (Details) - property	Sep. 30, 2021	Sep. 30, 2020
Real Estate Properties [Line Items]
Number of properties	83
Office
Real Estate Properties [Line Items]
Number of properties	71
Office | Wholly-owned properties
Real Estate Properties [Line Items]
Number of properties	53
Office | Consolidated JV properties
Real Estate Properties [Line Items]
Number of properties	16
Office | Unconsolidated Fund properties
Real Estate Properties [Line Items]
Number of properties	2	2
Multifamily
Real Estate Properties [Line Items]
Number of properties	12
Multifamily | Wholly-owned properties
Real Estate Properties [Line Items]
Number of properties	11
Multifamily | Consolidated JV properties
Real Estate Properties [Line Items]
Number of properties	1
Consolidated Portfolio
Real Estate Properties [Line Items]
Number of properties	81
Consolidated Portfolio | Office
Real Estate Properties [Line Items]
Number of properties	69
Consolidated Portfolio | Office | Wholly-owned properties
Real Estate Properties [Line Items]
Number of properties	53
Consolidated Portfolio | Office | Consolidated JV properties
Real Estate Properties [Line Items]
Number of properties	16
Consolidated Portfolio | Office | Unconsolidated Fund properties
Real Estate Properties [Line Items]
Number of properties	0
Consolidated Portfolio | Multifamily
Real Estate Properties [Line Items]
Number of properties	12
Consolidated Portfolio | Multifamily | Wholly-owned properties
Real Estate Properties [Line Items]
Number of properties	11
Consolidated Portfolio | Multifamily | Consolidated JV properties
Real Estate Properties [Line Items]
Number of properties	1