Stock-Based Compensation (Narrative) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
Mar. 31, 2012	Mar. 31, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation costs	$ 2.3	$ 2.3
Income tax benefits realized	0.7	0.7
Total fair value of restricted share awards vested during the period	2.4	2.5
Weighted-average estimated grant-date fair values of employee stock options granted (per share)	$ 25.89
Stock Option Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Pre-tax unrecognized compensation expense, net of estimated forfeitures	7.1
Weighted-average period of pre-tax unrecognized compensation expense for stock options to be recognized as expense, years	2.3
Total pre-tax intrinsic value of stock options exercised	2.2	4.5
Restricted Share Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Pre-tax unrecognized compensation expense, net of estimated forfeitures	$ 4.9
Weighted-average period of pre-tax unrecognized compensation expense for stock options to be recognized as expense, years	2.3

Employee service share-based compensation cost not yet recognized pre-tax, net of estimated forfeitures.

No definition available.

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- Definition

Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

+ References

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-Name Accounting Standards Codification

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-Name Staff Accounting Bulletin (SAB)

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- Definition

The weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, using a decimal to express in number of years.

+ References

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-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

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- Definition

The total recognized tax benefit related to compensation cost for equity-based payment arrangements recognized in income during the period.

+ References

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- Definition

The total fair value of equity-based awards for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

+ References

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- Definition

The total accumulated difference between fair values of underlying shares on dates of exercise and exercise price on options which were exercised (or share units converted) into shares during the reporting period under the plan.

+ References

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- Definition

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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