Revenue Recognition - Business Management Fees (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020	Sep. 30, 2020
Managed Operators
Related Party Transaction [Line Items]
Business management fee percent based on management agreements					0.60%
Aggregate business management fees	$ 5,374	$ 6,297	$ 11,012	$ 12,423
ABP Trust, AIC, The Industrial Fund and The Open End Fund
Related Party Transaction [Line Items]
Aggregate business management fees	$ 1,271	$ 687	$ 2,187	$ 1,240