Goodwill and Other Intangible Assets - Narrative (Details) - USD ($) $ in Millions	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017
Finite-Lived Intangible Assets [Line Items]
Amortization expense	$ 17.3	$ 18.1
Facility management contracts
Finite-Lived Intangible Assets [Line Items]
Weighted average period	1 year 5 months 24 days

The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
-Section 45
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-URI http://asc.fasb.org/extlink&oid=6388964&loc=d3e16225-109274

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