Income Taxes - Income Tax Expense Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Expected U.S. federal income taxes at statutory rate (percent)	21.00%	21.00%	24.60%
Partnership income not taxed at federal level (percent)	(2.30%)	(260.90%)	(6.40%)
Valuation allowance (percent)	71.40%	65.00%	(20.90%)
State and local income taxes, net of federal benefit (percent)	(6.50%)	26.90%	(6.40%)
Nondeductible expenses and other permanent items (percent)	(13.10%)	150.80%	(1.40%)
Revaluation of debt and other debt transaction differences (percent)	(0.059)	(0.490)	(0.072)
Federal tax rate change (percent)	0.00%	0.00%	10.20%
Change in liability for uncertain tax positions (percent)	(2.90%)	0.00%	0.00%
Federal tax credit (percent)	11.40%	0.00%	0.00%
Other (percent)	0.90%	0.30%	0.10%
Income tax expense (percent)	74.10%	(45.90%)	(7.30%)
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Expected U.S. federal income taxes at statutory rate	$ (792)	$ 81	$ (1,139)
Partnership income not taxed at federal level	85	(1,007)	294
Valuation allowance	(2,694)	251	965
State and local income taxes, net of federal benefit	244	104	295
Nondeductible expenses and other permanent items	496	582	66
Revaluation of debt and other debt transaction differences	222	(189)	332
Federal tax rate change	0	0	(471)
Change in liability for uncertain tax positions	108	0	0
Federal tax credits	(431)	0	0
Other	(33)	1	(5)
Income tax (benefit) expense	$ (2,795)	$ (177)	$ 337