Share Based Compensation (Additional Information) (Detail) - USD ($) shares in Millions, $ in Millions	9 Months Ended
Sep. 30, 2015	Sep. 30, 2014
Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options granted (in shares)	0.5	0.5
Total unrecognized compensation cost	$ 11.7
Weighted-average period of total unrecognized compensation cost, in years	1 year 6 months
Unvested Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted (in shares)	0.1	0.1
Total unrecognized compensation cost	$ 9.9
Weighted-average period of total unrecognized compensation cost, in years	1 year 1 month 6 days
Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted (in shares)	0.1	0.1
Total unrecognized compensation cost	$ 6.8
Weighted-average period of total unrecognized compensation cost, in years	1 year

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=6415400&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

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).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-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=6415400&loc=d3e5070-113901

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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

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(1)(iv)(1)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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