Share-Based Compensation and Benefit Plans - Additional Information (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
Dec. 31, 2012 Age CompensationPlan	Dec. 31, 2011	Dec. 31, 2010
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of share-based compensation plan	1
Percent of market price share-based compensation awards granted	100.00%
Shares awarded under plan	80,500
Stock options outstanding	324,150	385,150
Weighted-average grant date fair value	$ 12.90	$ 12.31	$ 11.45
Total intrinsic value of stock options exercised	$ 5,641	$ 4,724	$ 6,559
Fair value of stock options vested	315	475	597
Weighted-average grant date fair value of non-vested (restricted) stock	$ 69.66	$ 63.87	$ 49.43
Fair value of non-vested stock that vested	0	672	3,609
Stock delivered as payment to satisfy tax withholdings, shares		2,527	19,678
Stock delivered as payment to satisfy tax withholdings, market value		180	1,155
Share-based compensation	7,939	6,663	5,175
Cash received from Common stock issued	3,790	4,530	5,285
Tax benefit realized for the tax deductions from share-based compensation plans	1,245	916	3,083
Age of Chief Executive Officer when non-vested (restricted) stock vests	82
Number of days under which shares to be purchased by employee on such available	90 days
Discount allowed to employees to purchase share	5.00%
Average price of the shares purchased by employees	$ 68.76	$ 59.44	$ 51.69
Additional shares issued that resulted from cash dividends investment in common stock	15,411	5,097	5,812
Common stock issued to profit sharing retirement plan, shares	26,991	27,240	9,975
Common stock contribution to 401(k) plan	1,772	1,718	489
Non-Vested (Restricted) Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized share-based compensation expense	56,132
Weighted-average period for recognition of share-based compensation expense, in years	11 years 3 months 18 days
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized share-based compensation expense	1,317
Weighted-average period for recognition of share-based compensation expense, in years	1 year 7 months 6 days
Common Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock delivered as payment to satisfy tax withholdings, shares	29,987	7,616
Stock delivered as payment to satisfy tax withholdings, market value	2,229	437
Class B Common Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock delivered as payment to satisfy tax withholdings, shares			56,043
Stock delivered as payment to satisfy tax withholdings, market value			3,212
Class B Common Stock \| Non-Vested (Restricted) Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Obligation to issue non-vested restricted shares	80,543
Chief Executive Officer \| Non-Vested (Restricted) Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized share-based compensation expense	37,000
Weighted-average period for recognition of share-based compensation expense, in years	10 years
2001 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate awards, shares	4,000,000
Shares reserved for future grant	396,489
Stock options outstanding	324,150
2001 Plan \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Years in which options under 2001 Plan vest	2 years
Number of days under which shares to be purchased by employee on such available	5 years
2001 Plan \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Years in which options under 2001 Plan vest	5 years
Number of days under which shares to be purchased by employee on such available	10 years
2001 Plan \| Common Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares awarded under plan	1,955,912
2001 Plan \| Class B Common Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares awarded under plan	1,647,599
Espp
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate awards, shares	1,500,000
Shares reserved for future grant	532,895
Shares purchased under ESPP	6,753	8,520	8,515
Net proceeds from shares issued under ESPP	$ 1,522	$ 829	$ 757

Aggregate proceeds received by the entity during the annual period from exercises of stock or unit options and conversion of similar instruments granted under equity-based payment arrangements.

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As of the balance sheet date, the aggregate unrecognized cost of equity-based awards made to employees under equity-based compensation awards that have yet to vest.

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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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- Definition

The total recognized tax benefit related to compensation cost for equity-based payment arrangements recognized in income during the period.

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- Definition

The cash outflow paid by the company to cover an employee's income tax withholding obligation as part of a net-share settlement of a share-based award.

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The total cash inflow associated with the amount received from holders to acquire the entity's shares under incentive and share awards, including stock option exercises. This item inherently excludes any excess tax benefit, which the entity may have realized and reported separately.

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- Definition

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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- Definition

Estimated period over which an employee is required to provide service in exchange for the equity-based payment award, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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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 discount rate from market value on purchase date that participants pay for shares.

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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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The total fair value of equity-based awards for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

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- Definition

The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested).

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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

The total accumulated difference between fair values of underlying shares on dates of exercise and exercise price on options which were exercised (or share units converted) into shares during the reporting period under the plan.

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- Definition

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

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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

The number of shares reserved for issuance under stock option agreements awarded under the plan that validly exist and are outstanding as of the balance sheet date, including vested options.

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- Definition

Fair value of options vested. Excludes equity instruments other than options, for example, but not limited to, share units, stock appreciation rights, restricted stock.

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No definition available.

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- Definition

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

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- Definition

For net-share settlement of share-based awards when the employer settles employees' income tax withholding obligations, this element represents the number of shares the employees use to repay the employer.

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No definition available.

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Number of shares issued during the period to an employee benefit plan, such as a defined contribution or defined benefit plan.

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No definition available.

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Value of shares issued during the period to an employee benefit plan, such as a defined contribution or defined benefit plan.

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No definition available.

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Additional shares issued to employee stock purchase plan for dividend reinvestments.

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No definition available.

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Number of share based compensation plan.

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No definition available.

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Percent of market price that share based compensation awards are granted

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Share based compensation arrangement by share based payment award average price per share of shares purchased.

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No definition available.

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- Definition

Share Based Compensation Arrangement by Share Based Payment Awards Contractual Term

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Share based compensation arrangement by share based payment award shares obligated to issue.

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- Definition

Vesting age of chief executive officer.

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