Share-Based Payments (Narrative) (Details) - USD ($)	3 Months Ended
Mar. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation costs	$ 9,530,000
Unrecognized compensation costs, period for recognition	2 years 7 months 6 days
Maximum employee contribution, percentage	4.00%
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employer matching contribution, percentage	50.00%
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employer matching contribution, percentage	100.00%
Performance Share Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation costs	$ 11,688,000
Unrecognized compensation costs, period for recognition	2 years 2 months 12 days
Restricted Share Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation costs	$ 4,386,000
Unrecognized compensation costs, period for recognition	1 year 9 months 18 days
Deferred Share Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation costs	$ 0
Share unit liability	$ 4,068,000	$ 3,714,000

Employee Stock Purchase Plan, Employer Matching Contribution, Percent of Match

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- Definition

Employee Stock Purchase Plan, Maximum Annual Contributions Per Employee, Percent

+ References

No definition available.

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- Definition

Unrecognized cost of unvested share-based compensation awards.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (i)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

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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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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

Intrinsic value of equity-based compensation awards outstanding. Excludes stock and unit options.

+ References

No definition available.

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