Equity-Based Compensation (Schedule of Number of Awards and Weighted Average Grant Date Fair Value) (Details) - $ / shares	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017
Performance stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of awards (in shares)	135,540	108,748
Weighted average grant date fair value (in USD per share)	$ 33.60	$ 42.72
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of awards (in shares)	95,674	120,048
Weighted average grant date fair value (in USD per share)	$ 36.81	$ 37.14
Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of awards (in shares)	0	25,000
Weighted average grant date fair value (in USD per share)	$ 0.00	$ 42.35
Deferred stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of awards (in shares)	10,255	10,170
Weighted average grant date fair value (in USD per share)	$ 35.96	$ 34.42
Common shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of awards (in shares)	2,113	2,034
Weighted average grant date fair value (in USD per share)	$ 35.50	$ 34.42

The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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 (c)(2)(iii)(1)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

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The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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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.

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Gross number of share options (or share units) granted during the period.

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The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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