Shareholders' Equity - Unrecognized Compensation Cost (Details) $ in Millions	12 Months Ended
Dec. 31, 2017 USD ($)
Equity [Abstract]
Total unrecognized compensatoin cost related to unvested share-based payment awards	$ 47.4
Period for recognition of unrecognized compensation cost related to unvested share-based payment awards	1 year 4 months 24 days
Unrecognized compensation cost expected to be recognized as compensation expense
2018	$ 18.8
2019	19.6
2020	4.4
2021	4.5
2022	0.2
Total	$ 47.4

Unrecognized compensation cost expected to be recognized in year five of the five succeeding years.

No definition available.

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- Definition

Unrecognized compensation cost expected to be recognized in year four of the five succeeding years.

+ References

No definition available.

+ Details

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- Definition

Unrecognized compensation cost expected to be recognized in year one of the five succeeding years.

+ References

No definition available.

+ Details

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- Definition

Unrecognized compensation cost expected to be recognized in year three of the five succeeding years.

+ References

No definition available.

+ Details

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- Definition

Unrecognized compensation cost expected to be recognized in year two of the five succeeding years.

+ References

No definition available.

+ Details

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- Definition

Unrecognized cost of unvested share-based compensation awards.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (i)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

+ Details

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- References

No definition available.

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- Definition

Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

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- References

No definition available.

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