Share-Based Compensation - Stock Options, Summary of Other Information (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of options vested	$ 3.7	$ 3.2	$ 2.8
Tax benefit from exercise of stock options	$ 1.0	$ 5.3
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant-date fair value of stock options granted (in dollars per share)	$ 10.48	$ 8.52	$ 7.46
Total intrinsic value of options exercised	$ 7.8	$ 19.5	$ 4.9

Amount of tax benefit from exercise of stock options granted under share-based compensation arrangement.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2A
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=SL79508275-113901

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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

+ References

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-Publisher FASB
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-Section 50
-Paragraph 2
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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.

+ References

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Fair value of options vested. Excludes equity instruments other than options, for example, but not limited to, share units, stock appreciation rights, restricted stock.

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