Number of unvested shares.

No definition available.

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- Definition

Share based compensation arrangement by share based payment award award vesting percentage.

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No definition available.

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Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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Amount, after tax, of expense for award under share-based payment arrangement.

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No definition available.

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- Definition

Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

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Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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Amount of tax benefit for recognition of expense of award under share-based payment arrangement.

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Estimated period over which an employee is required to provide service in exchange for the equity-based payment award, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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- Definition

Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

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- Definition

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

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- Definition

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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- Definition

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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- Definition

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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- Definition

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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Per share or unit weighted-average fair value of nonvested award under share-based payment arrangement. Excludes share and unit options.

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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No definition available.

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- Definition

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

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- Definition

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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- Definition

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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- Definition

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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No definition available.

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- Definition

Number of fully vested and expected to vest exercisable options that may be converted into shares under option plan. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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- Definition

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 Plans (Information Regarding Restricted Shares) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
General vesting period (years)	3 years
Unearned compensation costs	$ 18.7	$ 23.4
Recognition of unearned compensation, (years)	1 year
Fair value of Restricted Shares vested	$ 26.4	16.8	$ 14.3
Stock-based compensation expense	27.3	23.9	19.9
Related income tax benefit	(6.2)	(5.4)	(4.5)
Net stock-based compensation expense	$ 21.1	$ 18.5	$ 15.4
Shares
Outstanding — beginning of year (in shares)	1,690,600
Granted (in shares)	730,065
Vested (in shares)	(587,301)
Canceled (in shares)	(459,707)
Outstanding — ending of year (in shares)	1,373,657	1,690,600
Weighted Average Grant-Date Fair Value
Outstanding — beginning of year (in dollars per share)	$ 46.71
Granted (in dollars per share)	46.56
Vested (in dollars per share)	45.02
Canceled (in dollars per share)	48.47
Outstanding — ending of year (in dollars per share)	$ 46.76	$ 46.71
Restricted Stock \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
General expiration period, from date of grant or time of termination (years)	1 year
General vesting period (years)	1 year
Restricted Stock \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
General expiration period, from date of grant or time of termination (years)	3 years
General vesting period (years)	3 years
Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
General vesting period (years)	36 months
Shares
Outstanding — ending of year (in shares)	539,000
Weighted Average Grant-Date Fair Value
Period for achieving performance targets on performance based units (years)	3 years
Estimated vesting of shares based on performance shares	537,000
Performance Shares \| Minimum
Weighted Average Grant-Date Fair Value
Vesting percentage of grants, depending on achievement of specific performance targets	0.00%
Estimated vesting of shares based on performance shares	0
Performance Shares \| Maximum
Weighted Average Grant-Date Fair Value
Vesting percentage of grants, depending on achievement of specific performance targets	200.00%
Estimated vesting of shares based on performance shares	1,078,000