Stock-Based Compensation Plans - Additional Information (Detail) $ in Millions	12 Months Ended
Dec. 31, 2017 USD ($) Directors Stock_Plan Executives shares	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option compensation	$ 4.1	$ 3.3	$ 3.7
Accrued liabilities	$ 104.1	95.4
Stock Options Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of active stock option plans \| Stock_Plan	5
Number of active stock option plans for employees \| Stock_Plan	2
Number of active stock option plans for non-employee directors \| Directors	1
Number of active stock option plans for key executives \| Executives	1
Expiration term for stock granted	10 years
Aggregate number of shares of common stock reserved for issuance which can be granted \| shares	2,640,000
Number exercisable and fully vested \| shares	62,102
Fully vested stock options with performance conditions attached \| shares	8,577
Stock option compensation	$ 4.2	3.3	3.7
Total intrinsic value exercised	2.9	2.8	2.4
Total compensation cost related to non-vested stock options not yet recognized	$ 5.6
Expected compensation cost recognized over the weighted-average period	1 year 10 months 25 days
Current tax benefit related to stock option compensation	$ 3.0
Cash tax benefit realized from stock option exercises		0.3	0.2
Stock Options Plan [Member] \| Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Range of stock vesting period	24 years
Stock Options Plan [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Range of stock vesting period	6 years
Stock Equivalent Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration term for stock granted	10 years
Fully vested stock options with performance conditions attached \| shares	39,705
Total intrinsic value exercised	$ 1.7	1.8	2.4
Expected compensation cost recognized over the weighted-average period	1 year 8 months 23 days
Accrued liabilities	$ 13.6
Number of exercisable SEUs \| shares	44,636
Compensation cost	$ 6.6	$ 4.7	$ 4.9
Stock Equivalent Units [Member] \| Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Range of stock vesting period	11 months
Stock Equivalent Units [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Range of stock vesting period	4 years

Number of active stock option plans.

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Number of active stock option plans for key executives.

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Share-based compensation shares authorized under stock equivalent units exercise price range number of exercisable options.

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Carrying value as of the balance sheet date of obligations incurred and payable, pertaining to costs that are statutory in nature, are incurred on contractual obligations, or accumulate over time and for which invoices have not yet been received or will not be rendered. Examples include taxes, interest, rent and utilities. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

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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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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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Unrecognized cost of unvested options awarded to employees as compensation.

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

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The aggregate amount of noncash, equity-based employee remuneration. This may include the value of stock or unit options, amortization of restricted stock or units, and adjustment for officers' compensation. As noncash, this element is an add back when calculating net cash generated by operating activities using the indirect method.

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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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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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The number of shares reserved for issuance pertaining to the outstanding exercisable stock options as of the balance sheet date in the customized range of exercise prices for which the market and performance vesting condition has been satisfied.

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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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