Segments - Summary of Certain Financial Data For Each of Segments (Details) - USD ($) $ in Millions		9 Months Ended	12 Months Ended
		Sep. 30, 2017	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
Segment Reporting Information [Line Items]
Net Service Revenues		$ 1,713.6	$ 2,404.6		$ 2,353.6
Adjusted EBITDA	[1]	217.2	305.1		300.1
Capital Expenditures		50.6	89.9		86.4
Net income (loss)		(14.0)	44.4		(15.1)
Interest expense		73.7	72.5		97.8
Income tax provision (benefit)		(9.2)	12.8		(66.2)
Depreciation expense		56.5	80.1	$ 75.3	75.3
Amortization expense		92.9	56.3		104.9
Establish public company financial reporting compliance	[2]	0.8	4.8		4.1
Business transformation and integration costs	[3]	10.8	17.5		25.5
Expenses related to initial public offering	[4]		1.0		6.8
Debt extinguishment	[5]				25.1
Equity-based compensation	[6]	3.8	15.7		28.8
Management fees	[7]	1.9			13.1
Corporate
Segment Reporting Information [Line Items]
Adjusted EBITDA	[1]	(46.0)	(58.6)		(68.4)
Capital Expenditures		5.2	13.9		36.0
Operating Segments | Maintenance Services
Segment Reporting Information [Line Items]
Net Service Revenues		1,278.3	1,813.4		1,774.8
Adjusted EBITDA	[1]	210.3	282.0		289.8
Capital Expenditures		40.3	65.4		45.5
Operating Segments | Development Services
Segment Reporting Information [Line Items]
Net Service Revenues		437.7	595.4		583.3
Adjusted EBITDA	[1]	52.9	81.7		78.7
Capital Expenditures		5.1	10.6		4.9
Eliminations
Segment Reporting Information [Line Items]
Net Service Revenues		$ (2.4)	$ (4.2)		$ (4.5)

[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, 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 in connection with the IPO and subsequent registration statements.

[5] Represents losses on the extinguishment of debt.

[6] Represents equity-based compensation expense recognized for equity incentive plans outstanding, including $19.6 related to the IPO in the fiscal year ended September 30, 2018.

[7] Represents fees paid pursuant to a monitoring agreement terminated on July 2, 2018 in connection with the completion of the IPO.