Performance term considered in granting performance share units.

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- Definition

Period considered to determine expected volatility of stock price.

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The weight of the implied volatility based on the exchange traded options for the Company's common stock used in the fair value assumptions of the stock options granted.

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No definition available.

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- Definition

Maximum term required for the restrictions to lapse on restricted stock.

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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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- Definition

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

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Cash received on stock transaction after deduction of issuance costs.

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Amount of noncash expense for share-based payment arrangement.

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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

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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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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Rate of weighted-average expected volatility for award under share-based payment 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

Gross number of share options (or share units) granted during the period.

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No definition available.

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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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- Definition

Number of options outstanding, including both vested and non-vested options.

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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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- Definition

Purchase price of common stock expressed as a percentage of its fair value.

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Share-Based Compensation Plans - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation	$ 24.2	$ 26.3	$ 27.8
Consideration received from share-based awards	7.4	7.0	5.2
Income tax benefit recognized related to share-based compensation	$ 1.7	$ 1.8	$ 4.5
Number of shares granted	156,000	174,000	122,000
Number of shares outstanding	788,000	723,000	672,000	574,000
Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Performance period range	3 years
Stock option
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation	$ 3.3	$ 4.0	$ 4.0
Share-based payment award vesting period	4 years
Expiration period	10 years
Fair value of options vested	$ 2.3	$ 2.3	$ 3.1
Total unrecognized compensation cost, net of estimated forfeitures	$ 2.0
Total unrecognized compensation cost, weighted-average period for recognition	1 year
Weighted average of daily historical volatility of Company's stock price, weight (as a percent)	75.00%
Period considered to determine expected volatility of stock price	5 years
Implied volatility based on exchange traded options for Company's common stock, weight (as a percent)	25.00%
Weighted-average grant-date fair value of options granted (in dollars per share)	$ 18.95	$ 17.78	$ 31.46
Stock option \| Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Purchase price (as a percent)	100.00%
Stock Appreciation Rights
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares granted	0	0
Number of shares outstanding	0	0
Deferred Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation	$ 1.3	$ 1.4	$ 1.9
Deferred Stock \| In Lieu of Annual Cash Retainer
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Granted (in shares)	1,432	1,275	5,551
Deferred Stock \| Additional Compensation for Board Service
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based payment award vesting period	1 year
Expiration period	3 years
Granted (in shares)	11,004	18,172	10,152
Restricted Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation	$ 15.7	$ 15.5	$ 13.3
Total unrecognized compensation cost, net of estimated forfeitures	$ 17.2
Total unrecognized compensation cost, weighted-average period for recognition	2 years
Granted (in shares)	200,000	236,000	145,000
Forfeited (in shares)	17,000	36,000	23,000
Term for restrictions to lapse	6 years
Restricted Stock \| Additional Compensation for Board Service
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Granted (in shares)	7,208	7,407	6,345
Forfeited (in shares)	1,666
Performance Shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation	$ 3.7	$ 5.2	$ 8.4