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.

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

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- Definition

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

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Amount of cash inflow from issuance of shares under share-based compensation arrangement. Issuance includes, but is not limited to, exercise of stock options and similar instruments.

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Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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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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The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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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.

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Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Stock-Based Compensation (Narrative) (Details) - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Additional shares available for issuance	2.7		2.7
Compensation cost recognized for stock-based awards	$ 2.5	$ 2.3	$ 5.4	$ 4.5
Income tax benefit recognized in the income statement for stock-based awards	$ 0.6	$ 0.9	1.3	1.6
Total cash received as a result of stock option exercises			3.4	8.1
Tax benefit realized as a result of stock option exercises and the vesting of other share-based awards			1.9	3.8
Total intrinsic value of stock options exercised			$ 2.2	$ 5.2
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Term of options			10 years
Employee Awards [Member] \| Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period			4 years
Employee Awards [Member] \| Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period			4 years
Employee Awards [Member] \| Performance-Based Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period			3 years
Non-Employee Awards [Member] \| Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period			1 year