Management Contracts Purchased - Additional Information (Detail)	Oct. 25, 2019 USD ($)	Oct. 26, 2018 USD ($)	Mar. 31, 2020 USD ($) Funds	Sep. 30, 2019 USD ($)
Contracts In Progress Costs And Earnings [Line Items]
Number of mutual funds | Funds			30
Management contracts impairment amount			$ 0	$ 0
Bp Capital Fund Advisors Llc [Member]
Contracts In Progress Costs And Earnings [Line Items]
Business combination, assets acquired and liabilities assumed, assets	$ 700,000	$ 200,000,000
Business combination, agreement date		Jul. 10, 2018
Business combination, cash paid	$ 700,000	$ 1,600,000
Business combination, consideration transferred, other		$ 100,000
Business acquisition, effective date of acquisition		Oct. 25, 2018