Income Taxes - Deferred Tax Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Sep. 30, 2019
Deferred tax assets:
Investment in partnership	$ 47,897	$ 40,880
Stock-based compensation	1,187	811
Deferred revenue	525	564
Accrued expenses	181	110
Net operating loss carryforwards	10,969	6,360
Section 163j carryforward	2,498	2,006
Federal tax credits	901	0
Other	73	42
Gross deferred tax assets	64,231	50,773
Valuation allowance	(20,230)	(16,609)
Deferred tax liabilities:
Intangible assets	(9,167)	(6,257)
Other	(291)	(285)
Net deferred tax asset	$ 34,543	$ 27,622