Share-based Compensation (Narrative) (Detail) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Proceeds from stock options exercised	$ 0.8	$ 1.6	$ 0.3
Awards granted (in shares)	0	0
Shares withheld for employee taxes	22,000	6,000	128,000
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total income tax benefit recognized related to restricted stock awards	$ 2.4	$ 1.4	$ 7.5
Compensation cost recognition weighted average period	1 year 8 months 12 days
Award vesting period	5 years
Share-based compensation arrangement, fair value of awards vested	$ 7.0	$ 3.7	4.7
Shares granted in period	22,000	43,000
Shares vested in period	26,000	32,000
Unrecognized compensation costs	$ 4.8
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee service share based compensation nonvested awards total compensation cost not yet recognized	$ 0.1
Compensation cost recognition weighted average period	1 year 1 month 6 days
Weighted-average remaining contractual life of options outstanding	5 years 3 months 18 days
Aggregate intrinsic value of options outstanding	$ 5.1
Weighted-average remaining contractual life of options exercisable	4 years 10 months 24 days
Aggregate intrinsic value of options exercisable	$ 3.6
Award vesting period	3 years
Award expiration period	10 years
Share-based compensation, shares authorized under stock option plans, exercise price range, lower range limit	$ 26.52
Share-based compensation, shares authorized under stock option plans, exercise price range, upper range limit	$ 66.68
Intrinsic value of options exercised	$ 5.9	$ 1.5	$ 1.0
Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost recognition weighted average period	1 year 9 months 18 days
Shares granted in period	40,610
Unrecognized compensation costs	$ 7.3

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

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Amount of cost to be recognized for nonvested award under share-based payment arrangement. Excludes share and unit options.

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

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Amount of cash inflow from exercise of option under 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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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 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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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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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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Gross number of share options (or share units) granted during the period.

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Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

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The floor of a customized range of exercise prices for purposes of disclosing shares potentially issuable under outstanding stock option awards on all stock option plans and other required information pertaining to awards in the customized range.

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The ceiling of a customized range of exercise prices for purposes of disclosing shares potentially issuable under outstanding stock option awards on all stock option plans and other required information pertaining to awards in the customized range.

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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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Amount of difference between fair value of the underlying shares reserved for issuance and exercise price of vested portions of options outstanding and currently exercisable.

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Weighted average remaining contractual term for vested portions of options outstanding and currently exercisable or convertible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Number of shares used to settle grantee's tax withholding obligation for award under share-based payment arrangement.

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