Segments - Summary of Certain Financial Data For Each of Segments (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Segment Reporting Information [Line Items]
Net service revenues		$ 651.9	$ 559.1	$ 1,206.3	$ 1,129.8
Adjusted EBITDA	[1]	66.8	38.9	119.3	90.5
Capital expenditures		18.2	20.6	27.9	35.1
Net income (loss)		6.3	(20.5)	(5.7)	(33.1)
Interest expense		9.6	17.1	23.1	34.5
Income tax expense (benefit)		2.3	(6.7)	(1.4)	(11.6)
Depreciation expense		20.7	19.3	42.3	39.5
Amortization expense		12.5	13.6	26.4	27.1
Establish public company financial reporting compliance	[2]				0.9
Business transformation and integration costs	[3]	6.2	8.9	12.8	17.3
Offering-related expenses	[4]		1.2	0.2	1.5
Equity-based compensation	[5]	5.3	4.9	10.2	13.3
COVID-19 related expenses	[6]	3.9	1.1	11.4	1.1
Severance and related costs			0.4	0.2	0.6
Business integration	[7]	2.1	3.5	5.7	8.9
IT infrastructure, transformation, and other	[8]	4.1	5.0	6.9	7.8
Corporate
Segment Reporting Information [Line Items]
Adjusted EBITDA	[1]	(16.4)	(16.0)	(30.5)	(31.2)
Capital expenditures		0.9	0.4	1.4	1.1
Operating Segments | Maintenance Services
Segment Reporting Information [Line Items]
Net service revenues		535.7	413.5	953.8	832.4
Adjusted EBITDA	[1]	72.3	40.7	121.9	88.4
Capital expenditures		15.3	14.3	24.2	26.1
Operating Segments | Development Services
Segment Reporting Information [Line Items]
Net service revenues		117.1	146.3	254.4	299.1
Adjusted EBITDA	[1]	10.9	14.2	27.9	33.3
Capital expenditures		2.0	5.9	2.3	7.9
Eliminations
Segment Reporting Information [Line Items]
Net service revenues		$ (0.9)	$ (0.7)	$ (1.9)	$ (1.7)

[1] Presented below is a reconciliation of Net income (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) vehicle fleet rebranding costs; (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.

[7] Represents isolated expenses specifically related to the integration of acquired companies such as one-time employee retention costs, employee onboarding and training costs, and fleet and uniform rebranding costs. The Company excludes Business integration costs from the measures disclosed above since such expenses vary in amount due to the number of acquisitions and size of acquired companies as well as factors specific to each acquisition, and as a result lack predictability as to occurrence and/or timing, and create a lack of comparability between periods.

[8] Represents expenses related to distinct initiatives, typically significant enterprise-wide changes. Such expenses are excluded from the measures disclosed above since such expenses vary in amount based on occurrence as well as factors specific to each of the activities, are outside of the normal operations of the business, and create a lack of comparability between periods.