Divestiture (Details) - Disposal Group, Disposed of by Sale, Not Discontinued Operations - Telapoint $ in Millions	12 Months Ended
Dec. 31, 2017 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net assets disposed of	$ 8.9
Consideration received	29.9
Pre-tax book gain on disposal	$ 21.0

Amount classified as assets attributable to disposal group held for sale or disposed of.

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Amount before tax of gain (loss) recognized on the sale or disposal of a disposal group. Excludes discontinued operations.

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