Segments - Summary of Certain Financial Data For Each of Segments (Details) - USD ($) $ in Millions		3 Months Ended
		Dec. 31, 2020	Dec. 31, 2019
Segment Reporting Information [Line Items]
Net service revenues		$ 554.4	$ 570.7
Adjusted EBITDA	[1]	52.4	51.7
Capital expenditures		9.7	14.5
Net (loss) income		(12.0)	(12.6)
Interest expense		13.6	17.4
Income tax (benefit)		(3.8)	(4.9)
Depreciation expense		21.6	20.2
Amortization expense		13.9	13.5
Establish public company financial reporting compliance	[2]		0.9
Business transformation and integration costs	[3]	6.4	8.3
Offering-related expenses	[4]	0.2	0.4
Equity-based compensation	[5]	5.0	8.5
COVID-19 related expenses	[6]	7.5
Corporate
Segment Reporting Information [Line Items]
Adjusted EBITDA	[1]	(14.3)	(15.1)
Capital expenditures		0.5	0.8
Operating Segments | Maintenance Services
Segment Reporting Information [Line Items]
Net service revenues		418.0	418.9
Adjusted EBITDA	[1]	49.6	47.7
Capital expenditures		8.9	11.7
Operating Segments | Development Services
Segment Reporting Information [Line Items]
Net service revenues		137.4	152.8
Adjusted EBITDA	[1]	17.1	19.1
Capital expenditures		0.3	2.0
Eliminations
Segment Reporting Information [Line Items]
Net service revenues		$ (1.0)	$ (1.0)

[1] Presented below is a reconciliation of Net (loss) to Adjusted EBITDA:

[2] Represents costs incurred to establish public company financial reporting compliance, including costs to comply with the requirements of Sarbanes-Oxley and the accelerated adoption of the revenue recognition standard (ASC 606 – Revenue from Contracts with Customers) and other miscellaneous costs.

[3] Business transformation and integration costs consist of (i) severance and related costs; (ii) rebranding of vehicle fleet; (iii) business integration costs and (iv) information technology infrastructure, transformation costs, and other.

[4] Represents transaction related expenses incurred for IPO related litigation and subsequent registration statements.

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

[6] Represents expenses related to the Company’s response to the COVID-19 pandemic, principally temporary and incremental salary and related expenses, personal protective equipment and cleaning and supply purchases, and other.