Stock Incentive Plans and Stock Purchase Plan - Additional Information (Detail) (USD $)	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for future grants and awards under Stock Incentive Plans	6,300,000
Stock-based compensation expense related to its stock incentive plans and stock purchase plan	$ 31,700,000	$ 31,300,000	$ 28,400,000
Aggregate fair value of restricted shares, vested	28,200,000	33,300,000	23,000,000
Weighted average grant-date fair value of restricted and deferred stock awards granted	$ 57.73	$ 46.48	$ 30.06
Stock-based compensation cost related to non-vested stock options remaining to be recognized as compensation expense, weighted-average period in years	1 year 4 months 24 days
Unrecognized Compensation Expense related to Nonvested Shares	26,100,000
Aggregate intrinsic value of stock options exercised	38,800,000	35,400,000	18,100,000
Excess tax benefit related to employee stock incentive plans	17,479,000	18,981,000	6,198,000
Cash proceeds received from the exercise of stock options	$ 30,100,000	$ 18,900,000	$ 20,800,000
Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of years over which options become exercisable on a pro rata basis	3 years
Stock Option [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period of options, maximum years	10 years
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of years over which options become exercisable on a pro rata basis	3 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	335,000
Shares issued under Stock Purchase Plan	260,000

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

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Amount of increase in additional paid in capital (APIC) resulting from a tax benefit associated with share-based compensation plan other than an employee stock ownership plan (ESOP). Includes, but is not limited to, excess tax benefit.

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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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Aggregate number of common shares reserved for future issuance.

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- Definition

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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- Definition

Unrecognized cost of unvested share-based awards, other than options, awarded to employees as compensation.

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- Definition

The aggregate cash inflow comprised of the amount received from (a) employees to acquire the entity's shares under incentive awards, including stock option exercises and restricted stock arrangements, and (b) the excess tax benefit arising from such transactions.

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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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- 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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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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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

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

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

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Number of shares issued during the period as a result of an employee stock purchase plan.

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