Income Taxes Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2018	Jun. 30, 2017
Income Tax Disclosure [Abstract]
Effective Income Tax Rate Reconciliation, Percent		21.00%	35.00%
Excess tax benefits associated with stock-based compensation	$ 0.9	$ 0.9	$ 1.1
Payments for Merger Related Costs	11.7	0.9
Unrecognized Tax Benefits	$ 3.9	$ 3.9

Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from share-based compensation.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32632-109319

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
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-Section 25
-Paragraph 20
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=96869850&loc=d3e28680-109314

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
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-Section 50
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-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32621-109319

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Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
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-Paragraph 13
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32698-109319

Reference 2: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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The amount of cash paid during the reporting period for charges associated with the mergers.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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Amount of unrecognized tax benefits.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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