Revenue Recognition - Business Management Fees (Details) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Managed Operating Companies
Related Party Transaction [Line Items]
Business management fee percent based on management agreements		0.60%
Aggregate business management fees	$ 6,976		$ 5,277	$ 17,988	$ 17,700
ABP Trust, AIC, The Industrial Fund and The Open End Fund
Related Party Transaction [Line Items]
Aggregate business management fees	$ 1,276		$ 686	$ 3,463	$ 1,926