Employee Incentive Plans, Unrecognized Compensation Cost (Details) $ in Millions	9 Months Ended
Sep. 30, 2017 USD ($)
Non-vested common shares and restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized Gross Compensation Costs (in millions of dollars)	$ 9.6
Expected Period (in years) Over Which the Remaining Gross Compensation Costs Will Be Recognized	2 years 7 months
TSR-Based Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized Gross Compensation Costs (in millions of dollars)	$ 5.6
Expected Period (in years) Over Which the Remaining Gross Compensation Costs Will Be Recognized	1 year 8 months
CP-Based Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized Gross Compensation Costs (in millions of dollars)	$ 6.1
Expected Period (in years) Over Which the Remaining Gross Compensation Costs Will Be Recognized	2 years 1 month
EVA-Based Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized Gross Compensation Costs (in millions of dollars)	$ 1.5
Expected Period (in years) Over Which the Remaining Gross Compensation Costs Will Be Recognized	2 years 5 months

Unrecognized cost of unvested share-based compensation awards.

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

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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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- 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.

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No definition available.

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