Share-Based Compensation (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Share-based Payment Arrangement [Abstract]
Fair value of share-based compensation awards, granted	$ 3.8	$ 0.7	$ 40.1	$ 33.5
Unrecognized compensation expense, net of estimated forfeitures, for unvested share-based compensation awards outstanding	63.2		$ 63.2
Weighted average recognition period for unrecognized compensation expense, in years			1 year 10 months 24 days
Share-based compensation expense	$ 9.4	$ 6.5	$ 22.6	$ 18.9

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 1
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-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5047-113901

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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- Definition

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

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
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- References

No definition available.

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- Definition

Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

+ References

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-Publisher FASB
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Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

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-Name Accounting Standards Codification
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