Summary of Significant Accounting Policies (Narrative) (Detail) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2017	Sep. 30, 2017	Sep. 30, 2016
Prior Period Reclassification Adjustment	$ 2.2	$ 29.9
Cumulative Effect on Retained Earnings, Tax			$ 7.7
Excess Tax Benefit from Share-based Compensation, Operating Activities		$ 0.2

Amount of the related income tax effect of a cumulative effect on retained earnings.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 9
-URI http://asc.fasb.org/extlink&oid=64853466&loc=d3e22663-107794

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- Definition

Amount of cash outflow for realized tax benefit related to deductible compensation cost reported on the entity's tax return for equity instruments in excess of the compensation cost for those instruments recognized for financial reporting purposes.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 20
-Section 55
-Paragraph 24
-URI http://asc.fasb.org/extlink&oid=65896087&loc=d3e11374-113907

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- Definition

The amount of a reclassification adjustment made to prior period financial statement amounts.

+ References

No definition available.

+ Details

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