Segments - Summary of Certain Financial Data For Each of Segments (Details) - USD ($) $ in Millions		3 Months Ended
		Dec. 31, 2024	Dec. 31, 2023
Segment Reporting Information [Line Items]
Net Service Revenues		$ 599.2	$ 626.7
Capital Expenditures		58.7	10.1
Segment Adjusted EBITDA	[1]	52.1	46.7
Interest expense, net		14.2	17.1
Depreciation expense		30.4	25.6
Amortization expense		8.1	10.1
Business transformation and integration costs		9.2	10.7
Equity-based compensation	[2]	4.8	5.3
(Loss) before income taxes		(14.6)	(22.1)
Operating Segments | Maintenance Services
Segment Reporting Information [Line Items]
Net Service Revenues		409.3	442.3
Capital Expenditures		41.7	8.6
Segment Adjusted EBITDA		34.6	31.4
Operating Segments | Development Services
Segment Reporting Information [Line Items]
Net Service Revenues		191.8	185.4
Capital Expenditures		17.0	1.5
Segment Adjusted EBITDA		17.5	15.3
Eliminations
Segment Reporting Information [Line Items]
Net Service Revenues		$ (1.9)	$ (1.0)

[1] Presented below is a reconciliation of (Loss) before income taxes to Segment Adjusted EBITDA:

[2] Represents equity-based compensation expense and related taxes recognized for equity incentive plans outstanding.