Supporting Financial Information - Intangible Assets, Net (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	$ 65,854	$ 64,412
Less accumulated amortization	(18,385)	(11,800)
Intangible assets, net	47,469	52,612
Amortization expense of intangibles	6,600	4,800
IBA
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	0	16,223
Customer contracts and related customer relationships
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	62,281	45,600
Less accumulated amortization	(17,378)	(11,150)
Covenants-not-to-compete
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	522	480
Less accumulated amortization	(264)	(212)
Trade name
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	3,051	2,109
Less accumulated amortization	$ (743)	$ (438)