Goodwill and Other Intangible Assets - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Services
Segment Reporting Information [Line Items]
Intangible asset amortization expense	$ 2.9	$ 3.3	$ 5.5	$ 6.3
Customer contracts and relationships
Segment Reporting Information [Line Items]
Weighted-average amortization period of intangible assets			8 years 1 month 6 days
Operating contracts and licenses
Segment Reporting Information [Line Items]
Weighted-average amortization period of intangible assets			25 years 10 months 24 days
Tradenames
Segment Reporting Information [Line Items]
Weighted-average amortization period of intangible assets			6 years 7 months 6 days
Non-compete agreements
Segment Reporting Information [Line Items]
Weighted-average amortization period of intangible assets			1 year 9 months 18 days
Other
Segment Reporting Information [Line Items]
Weighted-average amortization period of intangible assets			8 years 2 months 12 days