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Share-Based Payments (Summary of the Restricted Stock Unit Transactions under Share-Based Payment Plans) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash Incentive Plan [Member]
Weighted average remaining expense life	9 months
Share Based Compensation Liability Awards Amount Of Liability	$ 21.6	$ 37.0
Cash incentive unit payments made	$ 20.2	$ 14.2	$ 14.3
Restricted Stock Units (RSUs) [Member]
Unvested RSU awards at December 31, 2017	865,587
Granted in 2018, number of shares	303,550
Vested in 2018, number of shares	(303,606)
Forfeited in 2018, number of shares	(19,226)
Unvested RSU awards at December 31, 2018, number of shares	846,305	865,587
Unvested RSU awards at December 31, 2017, weighted average grant date fair value	$ 33.66
Granted in 2018, weighted average grant date fair value	55.96	$ 42.66	$ 32.53
Vested in 2018, weighted average grant date value	26.57
Forfeited in 2018, weighted average grant date fair value	42.62
Unvested RSU awards at December 31, 2018, weighted average grant date fair value	$ 44.00	$ 33.66
Total unrecognized compensation cost related to unvested RSU awards	$ 11.0
Weighted average remaining expense life	1 year 8 months
Total intrinsic value of shares vested	$ 18.0	$ 16.0	$ 12.6
Dividend Equivalent Units [Member]
Total intrinsic value of shares vested	$ 0.8	$ 0.9	$ 0.7

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- Definition

The liability recorded in connection with our Cash Incentive Plan.

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Unrecognized cost of unvested share-based compensation awards.

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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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The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

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Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event.

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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).

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The weighted average fair value at grant date for nonvested equity-based awards issued 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).

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The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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Amount of cash paid related to share-based compensation liabilities.

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The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

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The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan 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.

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