Acquisitions and Divestitures - 2017 Purchase Price Allocation (Details) - Acquisitions 2017 $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($)
Business Acquisition [Line Items]
Cash paid for acquisition of businesses	$ 108.2
Cash and cash equivalents	4.5
Amounts due to sellers	0.7
Non-monetary consideration	4.2
Purchase price	117.6
Assets acquired:
Cash and cash equivalents	4.5
Property and equipment	10.6
Goodwill and identifiable intangible assets	105.2
Other current and long-term assets	10.2
Liabilities assumed:
Accrued expenses and other current liabilities	(3.7)
Long-term liabilities and deferred tax liabilities	(9.1)
Purchase price	$ 117.6