Stock Incentive Plans and Stock Purchase Plans - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended
Mar. 31, 2013	Mar. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for future grants and awards under Stock Incentive Plans	4,300,000
Stock-based compensation expense related to its Stock Incentive Plans and Non-Qualified Plan	$ 7.3	$ 7.0
Net excess tax benefit recognized in additional paid-in capital related to the exercise of stock options and the vesting of restricted stock	$ 2.5
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period of options, maximum years	10
Number of years over which options become exercisable on a pro rata basis	3
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period of options, years	3 years
Deferred Stock Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period of options, years	5 years
1996 Non-Qualified Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of market value of common stock at which employees are permitted to purchase	85.00%
Percentage of discount received by participating employees	15.00%
Shares reserved for issuance	396,800
Shares issued under Non-Qualified Plan	26,641

Number of years over which options become exercisable on pro rata basis

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- Definition

Share based compensation arrangement by share based discount received by participating employees.

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Share based compensation arrangement by share based payment discounted market price.

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- Definition

Share-based compensation stock options exercisable period, maximum.

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- Definition

Tax benefit associated with any equity-based compensation plan other than an employee stock ownership plan (ESOP). The tax benefit results from the deduction by the entity on its tax return for an award of stock that exceeds the cumulative compensation cost for common stock or preferred stock recognized for financial reporting. Includes any resulting tax benefit that exceeds the previously recognized deferred tax asset (excess tax benefits).

+ References

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- Definition

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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-Name Staff Accounting Bulletin (SAB)

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-Section F

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- Definition

Aggregate number of common shares reserved for future issuance.

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- Definition

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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- Definition

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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- Definition

Number of share instruments newly issued under a share-based compensation plan.

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