Intangible Assets, Goodwill and Acquisitions - Schedule of Changes in Carrying Amount of Goodwill (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
Sep. 30, 2017	Sep. 30, 2018
Goodwill [Line Items]
Beginning balance	$ 1,667,114	$ 1,703,773
Acquisitions	36,659	62,988
Ending balance	1,703,773	1,766,761
Maintenance Services
Goodwill [Line Items]
Beginning balance	1,486,640	1,523,299
Acquisitions	36,659	49,064
Ending balance	1,523,299	1,572,363
Development Services
Goodwill [Line Items]
Beginning balance	180,474	180,474
Acquisitions		13,924
Ending balance	$ 180,474	$ 194,398

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=77989000&loc=SL49117168-202975

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Amount of increase in asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized resulting from a business combination.

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