Business Acquisitions - Additional Information (Details) $ in Thousands	12 Months Ended
	Sep. 30, 2021 USD ($) acquisition plant	Sep. 30, 2020 USD ($) acquisition	Sep. 30, 2019 USD ($) acquisition	Jul. 30, 2021 plant	Jul. 30, 2021 facility
Business Acquisition [Line Items]
Number of manufacturing plants | plant	2
Goodwill	$ 85,422	$ 46,348	$ 38,546
Purchase price allocation, maximum valuation period	1 year
Interest expense	$ 1,300
North Carolina Acquisitions - Final
Business Acquisition [Line Items]
Number of production and paving companies acquired | acquisition	5
Number of plants added | plant	14
Number of businesses acquired | acquisition	6
Total consideration transferred	$ 97,885
Goodwill	33,320
General and administrative expenses	600
North Carolina Acquisitions Provisional
Business Acquisition [Line Items]
Total consideration transferred	31,200
Goodwill	2,600
General and administrative expenses	300
Alabama Acquisition - Provisional
Business Acquisition [Line Items]
Total consideration transferred	81,682
Goodwill	3,157
General and administrative expenses	400
Number of aggregate facilities				4	4
All Acquisitions for Fiscal Year
Business Acquisition [Line Items]
Number of businesses acquired | acquisition		2	2
Total consideration transferred	210,734	$ 27,500	$ 13,900
Goodwill	39,074	$ 7,800	$ 5,600
Revenues since acquisition date	79,300
Net loss	$ (4,900)