Provision for Impairment of Investment Properties - Impairment Indicators (Details) - property	Sep. 30, 2020	Sep. 30, 2019
Impaired Long-Lived Assets Held and Used [Line Items]
Number of properties for which indicators of impairment were identified	3	2
Number of properties for which an impairment charge was recorded	1	1
Number of properties held for sale with impairment indicators but not impaired	0	0
Remaining properties with impairment indicators but not impaired	2	1
Weighted average percentage by which projected undiscounted cash flows exceeded carrying value for remaining properties	141.00%	20.00%
Number of properties with impairment indicators which were subsequently sold		1