SEGMENTS - Summary of Residential and Commercial Segment Reporting Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Segment Reporting Information [Line Items]
Net Sales	$ 1,441,448	$ 1,370,316	$ 1,355,586
Segment Adjusted EBITDA
Total Adjusted EBITDA for reporting segments	379,341	283,838	290,385
Adjustments to income before income tax provision
Capital Expenditures	77,147	88,545	170,938
Depreciation and amortization	129,042	132,544	118,533
Goodwill	967,816	994,271	993,995
Total Assets	2,167,711	2,343,876	2,371,627
Depreciation and amortization	(129,042)	(132,544)	(118,533)
Stock-based compensation costs	(25,835)	(18,704)	(18,105)
Acquisition and divestiture costs	(1,284)	(6,890)	(13,406)
Gain on sale of business	37,688	0	0
Secondary offering costs	0	(1,065)	0
Inventories	0	0	(19,297)
Other costs	(11,091)	(843)	(2,764)
Interest expense, net	(40,253)	(39,293)	(24,956)
Income before income taxes	209,524	84,499	93,324
Acquisition costs	500	3,900	11,500
Divestiture related costs	500	3,000	500
Inventory step up adjustments relating to business acquisitions	300		1,400
Costs related to restatement	5,900
Costs for process improvement	2,400
Costs of reduction in workforce	300	500	1,600
Legal expenses	1,800	300	900
Other costs	700		200
Costs related to an incentive plan			100
Residential
Segment Adjusted EBITDA
Total Adjusted EBITDA for reporting segments	365,273	252,830	250,130
Residential | Operating Segments
Segment Reporting Information [Line Items]
Net Sales	1,368,813	1,222,866	1,168,751
Segment Adjusted EBITDA
Total Adjusted EBITDA for reporting segments	365,273	252,830	250,130
Adjustments to income before income tax provision
Capital Expenditures	76,755	84,224	165,293
Depreciation and amortization	127,102	123,755	109,201
Goodwill	953,882	953,882	953,606
Total Assets	2,093,486	2,151,011	2,184,803
Depreciation and amortization	(127,102)	(123,755)	(109,201)
Commercial
Segment Adjusted EBITDA
Total Adjusted EBITDA for reporting segments	14,068	31,008	40,255
Commercial | Operating Segments
Segment Reporting Information [Line Items]
Net Sales	72,635	147,450	186,835
Segment Adjusted EBITDA
Total Adjusted EBITDA for reporting segments	14,068	31,008	40,255
Adjustments to income before income tax provision
Capital Expenditures	392	4,321	5,645
Depreciation and amortization	1,940	8,789	9,332
Goodwill	13,934	40,389	40,389
Total Assets	74,225	192,865	186,824
Depreciation and amortization	$ (1,940)	$ (8,789)	$ (9,332)