Deferred Tax Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2019
Deferred tax assets
Investment in partnership	$ 14,443	$ 40,880
Stock-based compensation	186	811
Tax receivable agreement	193	0
Deferred revenue	571	564
Accrued expenses	29	110
Net operating loss carryforwards	1,775	6,360
Section 163j carryforward	0	2,006
Other	33	42
Gross deferred tax assets	17,230	50,773
Valuation Allowance	(15,517)	(16,609)
Deferred tax liabilities
Intangible assets	(1,656)	(6,257)
Other	(5)	(285)
Net deferred tax asset	52	$ 27,622
Decrease to Investment in Partnership
Valuation Allowance [Line Items]
Immaterial adjustment to prior year amount	7,515
Decrease to Valuation Allowance
Valuation Allowance [Line Items]
Immaterial adjustment to prior year amount	7,515
Increase to Net Operating Loss Carryforwards
Valuation Allowance [Line Items]
Immaterial adjustment to prior year amount	1,672
Increase to Valuation Allowance
Valuation Allowance [Line Items]
Immaterial adjustment to prior year amount	$ 1,672