Segments - Summary of Certain Financial Data For Each of Segments (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Segment Reporting Information [Line Items]
Net service revenues		$ 596,637	$ 590,382	$ 1,122,650	$ 1,141,471
Adjusted EBITDA	[1]	61,102	51,621	111,223	118,043
Capital expenditures		25,281	14,307	42,610	44,095
Net loss		(3,606)	(22,064)	(12,433)	(2,740)
Interest expense		18,945	25,069	36,069	49,982
Income tax benefit		(1,315)	(7,858)	(4,451)	(59,397)
Depreciation expense		21,687	17,731	40,968	38,803
Amortization expense		13,807	29,318	28,938	60,364
Establish public company financial reporting compliance	[2]	1,308	185	1,692	2,816
Business transformation and integration costs	[3]	4,664	2,125	8,921	18,934
Expenses related to initial public offering	[4]		2,130		2,130
Equity-based compensation	[5]	5,612	4,276	11,519	5,802
Management fees	[6]		709		1,348
Corporate
Segment Reporting Information [Line Items]
Adjusted EBITDA	[1]	(14,888)	(19,542)	(30,491)	(34,180)
Capital expenditures		2,883	640	5,936	22,855
Operating Segments | Maintenance Services
Segment Reporting Information [Line Items]
Net service revenues		473,314	460,105	865,847	866,795
Adjusted EBITDA	[1]	64,957	58,282	113,663	118,892
Capital expenditures		18,932	12,805	30,014	19,467
Operating Segments | Development Services
Segment Reporting Information [Line Items]
Net service revenues		123,977	131,018	258,373	276,241
Adjusted EBITDA	[1]	11,033	12,881	28,051	33,331
Capital expenditures		3,466	862	6,660	1,773
Eliminations
Segment Reporting Information [Line Items]
Net service revenues		$ (654)	$ (741)	$ (1,570)	$ (1,565)

[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 (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.

[5] Represents equity-based compensation expense recognized for equity incentive plans outstanding, including $3,058 and $7,015 related to the IPO during the three and six months ended March 31, 2019, respectively.

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