Supporting Financial Information - Intangible Assets (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Sep. 30, 2020
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	$ 65,854		$ 64,412
Total accumulated amortization	(13,446)		(11,800)
Intangible assets, net	$ 52,408		52,612
Estimated useful live of intangible assets	10 years
Amortization expense of intangible assets	$ 1,600	$ 1,200
IBA
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	17,700		16,223
Customer contracts and related customer relationships
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	62,281		45,600
Total accumulated amortization	(12,707)		(11,150)
Customer contracts and related customer relationships | IBA
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	16,700
Covenants not to compete
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	522		480
Total accumulated amortization	(225)		(212)
Covenants not to compete | IBA
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	100
Trade name
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	3,051		2,109
Total accumulated amortization	(514)		$ (438)
Trade name | IBA
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	$ 900