Business Combinations - Intangible Assets Acquired (Details) $ in Millions	9 Months Ended
Sep. 30, 2018 USD ($)
Finite-Lived Intangible Assets, Gross [Abstract]
Aggregate Acquisitions	$ 10.3
Customer relationships
Finite-Lived Intangible Assets, Gross [Abstract]
Weighted Average Useful Life	5 years
Aggregate Acquisitions	$ 8.2
Customer backlog
Finite-Lived Intangible Assets, Gross [Abstract]
Weighted Average Useful Life	1 year
Aggregate Acquisitions	$ 1.4
Non-compete agreements
Finite-Lived Intangible Assets, Gross [Abstract]
Weighted Average Useful Life	5 years
Estimated Useful Life	5 years
Aggregate Acquisitions	$ 0.2
Trade name
Finite-Lived Intangible Assets, Gross [Abstract]
Weighted Average Useful Life	1 year
Estimated Useful Life	1 year
Aggregate Acquisitions	$ 0.1
Internally developed software
Finite-Lived Intangible Assets, Gross [Abstract]
Weighted Average Useful Life	3 years
Estimated Useful Life	3 years
Aggregate Acquisitions	$ 0.4
Minimum \| Customer relationships
Finite-Lived Intangible Assets, Gross [Abstract]
Estimated Useful Life	5 years
Minimum \| Customer backlog
Finite-Lived Intangible Assets, Gross [Abstract]
Estimated Useful Life	1 year
Maximum \| Customer relationships
Finite-Lived Intangible Assets, Gross [Abstract]
Estimated Useful Life	6 years
Maximum \| Customer backlog
Finite-Lived Intangible Assets, Gross [Abstract]
Estimated Useful Life	1 year 6 months

Useful life of finite-lived intangible assets acquired either individually or as part of a group of assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

No definition available.

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- Definition

Weighted average amortization period of finite-lived intangible assets acquired either individually or as part of a group of assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=66006027&loc=d3e16265-109275

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- References

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- Definition

Amount of increase in assets, excluding financial assets, lacking physical substance with a definite life, from an acquisition.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=66006027&loc=d3e16265-109275

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