Significant Non-cash Transactions (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Jun. 25, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Other Significant Noncash Transactions [Line Items]
Equity issued as part of acquisitions' purchase consideration		$ 0	$ 0	$ 104
Acquisition date fair value of contingent consideration in connection with business combinations		4,748	13,032	2,084
Replacement of prior senior secured credit facility with senior secured credit facility		0	100,229	87,525
Mezzanine Notes net settled with Mezzanine Warrant exercises		0	0	14
Unsecured notes payable to related and unrelated creditors net settled with Junior Subordinated Notes Warrants		0	0	2,565
Settlement of warrant liability with equity as a result of Mezzanine Warrant exercise		0	0	9,253
Preferred return on redeemable class A units and class A units	$ 0
Debt issuance costs financed with proceeds from senior secured credit facility		0	1,271	904
Conversion of notes payable to related and unrelated creditors to Class A common stock		0	0	8,054
Redeemable Class A Common Stock
Other Significant Noncash Transactions [Line Items]
Preferred return on redeemable class A units and class A units		0	0	552
Class A Common Stock
Other Significant Noncash Transactions [Line Items]
Preferred return on redeemable class A units and class A units		0	0	2,522
Restricted Class A Common Stock
Other Significant Noncash Transactions [Line Items]
Equity issued as part of acquisitions' purchase consideration		$ 0	$ 225	$ 550