Segments - Summary of Certain Financial Data For Each of Segments (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Segment Reporting Information [Line Items]
Net service revenues		$ 657,209	$ 630,330	$ 1,779,859	$ 1,771,800
Adjusted EBITDA	[1]	101,908	97,833	213,131	215,876
Capital expenditures		34,616	27,648	77,225	71,743
Net income (loss)		31,709	(1,397)	19,276	(4,139)
Interest expense		18,360	27,499	54,429	77,481
Income tax expense (benefit)		11,033	1,247	6,582	(58,150)
Depreciation expense		20,884	17,839	61,851	56,642
Amortization expense		13,936	29,247	42,873	89,611
Establish public company financial reporting compliance	[2]	1,140	555	2,832	3,372
Business transformation and integration costs	[3]	4,431	2,466	13,354	21,402
Expenses related to initial public offering	[4]	108	4,678	108	6,808
Equity-based compensation	[5]	307	14,951	11,826	20,753
Management fees	[6]		748		2,096
Corporate
Segment Reporting Information [Line Items]
Adjusted EBITDA	[1]	(16,196)	(15,469)	(46,687)	(49,649)
Capital expenditures		6,940	11,174	12,874	34,029
Operating Segments | Maintenance Services
Segment Reporting Information [Line Items]
Net service revenues		492,105	474,581	1,357,952	1,341,375
Adjusted EBITDA	[1]	91,138	91,349	204,800	210,241
Capital expenditures		24,434	14,292	54,449	33,759
Operating Segments | Development Services
Segment Reporting Information [Line Items]
Net service revenues		166,319	157,379	424,692	433,620
Adjusted EBITDA	[1]	26,966	21,953	55,018	55,284
Capital expenditures		3,242	2,182	9,902	3,955
Eliminations
Segment Reporting Information [Line Items]
Net service revenues		$ (1,215)	$ (1,630)	$ (2,785)	$ (3,195)

[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 new revenue recognition standard (ASU 2014-09 – 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 the IPO in fiscal 2018 and subsequent registration statements.

[5] Represents equity-based compensation expense recognized for equity incentive plans outstanding, including $7,328 related to the IPO during the nine months ended June 30, 2019.

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