Overview - Schedule of Properties Portfolio (Details) - property	Mar. 31, 2020	Mar. 31, 2019
Real Estate Properties [Line Items]
Number of properties	83
Office
Real Estate Properties [Line Items]
Number of properties	72
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	17
Office | Unconsolidated Fund properties
Real Estate Properties [Line Items]
Number of properties	2	8
Multifamily
Real Estate Properties [Line Items]
Number of properties	11
Multifamily | Wholly-owned properties
Real Estate Properties [Line Items]
Number of properties	10
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	70
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	17
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	11
Consolidated Portfolio | Multifamily | Wholly-owned properties
Real Estate Properties [Line Items]
Number of properties	10
Consolidated Portfolio | Multifamily | Consolidated JV properties
Real Estate Properties [Line Items]
Number of properties	1