Supporting Financial Information - Intangible Assets, Net (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	$ 64,412	$ 48,189
Less accumulated amortization	(11,800)	(6,981)
Intangible assets, net	52,612	41,208
Amortization expense of intangibles	4,800	2,700
IBA
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	16,223	0
Customer contracts and related customer relationships
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	45,600	45,600
Less accumulated amortization	(11,150)	(6,590)
Covenants not to compete
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	480	480
Less accumulated amortization	(212)	(164)
Trade name
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	2,109	2,109
Less accumulated amortization	$ (438)	$ (227)