Share-Based Compensation (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Fair value of share-based compensation awards, granted	$ 1.9	$ 1.7	$ 36.3	$ 32.8
Unrecognized compensation expense, net of estimated forfeitures, for unvested share-based compensation awards outstanding	68.7		$ 68.7
Weighted average recognition period for unrecognized compensation expense, in years			2 years 1 month 6 days
Share-based compensation expense	$ 6.9	$ 6.5	$ 13.2	$ 12.4

Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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- Definition

The total fair value of shares issued during the period under a deferred compensation arrangement.

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Unrecognized cost of unvested share-based compensation awards.

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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.

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