Segments - Summary of Certain Financial Data For Each of Segments (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Segment Reporting Information [Line Items]
Net service revenues		$ 608.1	$ 657.2	$ 1,737.9	$ 1,779.9
Adjusted EBITDA	[1]	91.0	101.9	181.6	213.1
Capital expenditures		10.8	34.6	45.9	77.2
Net (loss) income		(2.4)	31.7	(35.5)	19.3
Interest expense		15.4	18.4	49.9	54.4
Income tax (benefit) expense		(0.3)	11.0	(11.9)	6.6
Depreciation expense		20.9	20.9	60.4	61.9
Amortization expense		13.6	13.9	40.6	42.9
Establish public company financial reporting compliance	[2]		1.1	0.9	2.8
Business transformation and integration costs	[3]	8.2	4.5	25.8	13.3
Offering-related expenses	[4]	2.6	0.1	4.1	0.1
Equity-based compensation	[5]	4.9	0.3	18.2	11.8
COVID-19 related expenses	[6]	4.0		5.0
Changes in self-insured liability estimates	[7]	24.1		24.1
Corporate
Segment Reporting Information [Line Items]
Adjusted EBITDA	[1]	(14.1)	(16.2)	(45.2)	(46.7)
Capital expenditures		1.2	7.0	2.4	12.9
Operating Segments | Maintenance Services
Segment Reporting Information [Line Items]
Net service revenues		460.0	492.1	1,295.1	1,358.0
Adjusted EBITDA	[1]	84.0	91.1	172.9	204.8
Capital expenditures		8.0	24.4	34.0	54.4
Operating Segments | Development Services
Segment Reporting Information [Line Items]
Net service revenues		149.1	166.3	445.5	424.7
Adjusted EBITDA	[1]	21.1	27.0	53.9	55.0
Capital expenditures		1.6	3.2	9.5	9.9
Eliminations
Segment Reporting Information [Line Items]
Net service revenues		$ (1.0)	$ (1.2)	$ (2.7)	$ (2.8)

[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 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, including $1.9 and $5.8 million of equity based compensation expense related to the IPO in the three and nine months ended June 30, 2020, respectively.

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

[7] Represents expenses related to changes in estimates and actuarial assumptions associated with the Company’s self-insured liability amounts for workers’ compensation, general liability, auto liability, and employee health care insurance programs, to reflect uncertainties associated with the current environment, including the COVID-19 pandemic.