Income Taxes - Narrative (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended	12 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Income Tax Examination [Line Items]
Asset Impairment Charges			$ 24.8	$ 0.0
Statutory rate	21.00%	35.00%	21.00%	35.00%	35.00%
Effect of tax cuts and jobs act - Deferred Federal Income Tax Expense (Benefit)	$ 1.0		$ 1.3
Additions for tax positions of prior years			1.6	$ 0.2
Unrecognized tax benefits including interest and penalties that would affect the Company's effective tax rate if recognized	10.1	$ 5.7	10.1	5.7
Total accrued interest and penalties related to uncertain tax positions	4.5		4.5		$ 4.1
Increase (decrease) in income tax expense related to interest and penalties on unrecognized tax benefits	0.1	$ 0.1	0.4	$ (5.2)
Settlement with taxing authority and lapse in statute of limitations
Income Tax Examination [Line Items]
Reasonably possible decrease in unrecognized federal and state tax benefits within twelve months	$ (6.2)		$ (6.2)

Effect of tax cuts and jobs act - Deferred Federal Income Tax Expense (Benefit)

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Amount of write-down of assets recognized in the income statement. Includes, but is not limited to, losses from tangible assets, intangible assets and goodwill.

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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The amount of the unrecognized tax benefit of a position taken for which it is reasonably possible that the total amount thereof will significantly increase or decrease within twelve months of the balance sheet date.

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Amount accrued for interest on an underpayment of income taxes and penalties related to a tax position claimed or expected to be claimed in the tax return.

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Amount of expense for interest on an underpayment of income taxes and penalties related to a tax position claimed or expected to be claimed in the tax return.

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Amount of increase in unrecognized tax benefits resulting from tax positions taken in prior period tax returns.

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The total amount of unrecognized tax benefits that, if recognized, would affect the effective tax rate.

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