Significant Non-cash Transactions (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Other Significant Noncash Transactions [Line Items]
Debt converted to shares issued	$ 0	$ 8,054	$ 0
Equity issued as part of acquisitions' purchase consideration	0	104	275
Acquisition date fair value of contingent consideration in connection with business combinations	13,032	2,084	1,221
Replacement of prior Senior Secured Credit Facility with Senior Secured Credit Facility	100,229	87,525	0
Mezzanine Notes net settled with Mezzanine Warrant exercises	0	14	0
Unsecured notes payable to related and unrelated creditors net settled with Junior Subordinated Notes Warrants	0	2,565	0
Settlement of warrant liability with equity as a result of Mezzanine Warrant exercise	0	9,253	0
Preferred return on Class A Units and Redeemable Class A Units			756
Debt issuance costs financed with proceeds from Senior Secured Credit Facility	1,271	904	0
Redeemable Class A Common Stock
Other Significant Noncash Transactions [Line Items]
Preferred return on Class A Units and Redeemable Class A Units	0	552	701
Class A Common Stock
Other Significant Noncash Transactions [Line Items]
Preferred return on Class A Units and Redeemable Class A Units	0	2,522	2,223
Restricted Stock
Other Significant Noncash Transactions [Line Items]
Equity issued as part of acquisitions' purchase consideration	225	550	0
Junior Subordinated Notes
Other Significant Noncash Transactions [Line Items]
Debt converted to shares issued	$ 0	$ 0	$ 500