Summary of Significant Accounting Policies - Accounts Receivable and Allowance for Doubtful Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Allowance for doubtful accounts [Roll Forward]
Balance, beginning of period	$ 583	$ 2,377
Amount of charge (benefit) to expense	76
Amount of charge (benefit) to expense		(1,122)
Deductions and adjustments	(132)	(672)
Balance, end of period	$ 527	$ 583