Business Combinations Intangible Assets Acquired (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Finite-Lived Intangible Assets, Gross [Abstract]
Aggregate Acquisitions	$ 4.6	$ 12.9
Customer relationships
Finite-Lived Intangible Assets, Gross [Abstract]
Weighted Average Useful Life (in years)	7 years	5 years
Estimated Useful Life (in years)	7 years
Aggregate Acquisitions	$ 3.7	$ 10.6
Customer backlog
Finite-Lived Intangible Assets, Gross [Abstract]
Weighted Average Useful Life (in years)	9 months	1 year
Estimated Useful Life (in years)	9 months
Aggregate Acquisitions	$ 0.4	$ 1.5
Non-compete agreements
Finite-Lived Intangible Assets, Gross [Abstract]
Weighted Average Useful Life (in years)	5 years	5 years
Estimated Useful Life (in years)	5 years
Aggregate Acquisitions	$ 0.1	$ 0.3
Trade name
Finite-Lived Intangible Assets, Gross [Abstract]
Weighted Average Useful Life (in years)	1 year	1 year
Estimated Useful Life (in years)	1 year	1 year
Aggregate Acquisitions	$ 0.1	$ 0.1
Developed software
Finite-Lived Intangible Assets, Gross [Abstract]
Weighted Average Useful Life (in years)	3 years	3 years
Estimated Useful Life (in years)	3 years	3 years
Aggregate Acquisitions	$ 0.3	$ 0.4
Minimum | Customer relationships
Finite-Lived Intangible Assets, Gross [Abstract]
Estimated Useful Life (in years)		5 years
Minimum | Customer backlog
Finite-Lived Intangible Assets, Gross [Abstract]
Estimated Useful Life (in years)		1 year
Minimum | Non-compete agreements
Finite-Lived Intangible Assets, Gross [Abstract]
Estimated Useful Life (in years)		4 years
Maximum | Customer relationships
Finite-Lived Intangible Assets, Gross [Abstract]
Estimated Useful Life (in years)		6 years
Maximum | Customer backlog
Finite-Lived Intangible Assets, Gross [Abstract]
Estimated Useful Life (in years)		1 year 6 months
Maximum | Non-compete agreements
Finite-Lived Intangible Assets, Gross [Abstract]
Estimated Useful Life (in years)		5 years