Segments - Summary of Certain Financial Data For Each of Segments (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Segment Reporting Information [Line Items]
Net service revenues		$ 630,330	$ 627,490	$ 1,771,800	$ 1,658,864
Adjusted EBITDA	[1]	97,833	98,479	215,876	186,783
Capital expenditures		27,648	18,635	71,743	51,022
Net (loss) income		(1,397)	15,402	(4,139)	(37,873)
Interest expense		27,499	24,922	77,481	73,372
Income tax provision (benefit)		1,247	1,102	(58,150)	(22,037)
Depreciation		17,839	19,919	56,642	60,740
Amortization expense		29,247	31,250	89,611	94,800
Establish public company financial reporting compliance	[2]	555	407	3,372	2,379
Business transformation and integration costs	[3]	2,466	2,645	21,402	10,808
Expenses related to initial public offering	[4]	4,678		6,808
Equity-based compensation	[5]	14,951	2,193	20,753	2,637
Management fees	[6]	748	639	2,096	1,957
Corporate
Segment Reporting Information [Line Items]
Adjusted EBITDA	[1]	(15,469)	(15,257)	(49,649)	(53,746)
Capital expenditures		11,174	1,556	34,029	4,000
Operating Segments | Maintenance Services
Segment Reporting Information [Line Items]
Net service revenues		474,581	461,191	1,341,375	1,233,222
Adjusted EBITDA	[1]	91,349	90,371	210,241	181,155
Capital expenditures		14,292	15,086	33,759	42,663
Operating Segments | Development Services
Segment Reporting Information [Line Items]
Net service revenues		157,379	166,945	433,620	427,344
Adjusted EBITDA	[1]	21,953	23,365	55,284	59,374
Capital expenditures		2,182	1,993	3,955	4,359
Eliminations
Segment Reporting Information [Line Items]
Net service revenues		$ (1,630)	$ (646)	$ (3,195)	$ (1,702)

[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 new 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 in connection with the IPO.

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

[6] Represents management fees paid to our Sponsors pursuant to the Monitoring Agreement.