Stock-Based Compensation Plans - Summary of Activity Related to Company's Restricted Stock (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unvested share, beginning of period, Shares	84	129	132
Granted, Shares	59	52	98
Vested, Shares	(78)	(97)	(101)
Unvested shares, end of period, Shares	65	84	129
Weighted-Avg. Grant-Date Fair Value, beginning of period, Unvested Shares	$ 29	$ 19	$ 21
Weighted-Avg. Grant-Date Fair Value, Granted	$ 45	$ 38	$ 20
Weighted-Avg. Grant-Date Fair Value, Vested	$ 30	$ 21	$ 22
Weighted-Avg. Grant-Date Fair Value, end of period, Unvested Shares	$ 42	$ 29	$ 19

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 number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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- Definition

The weighted average fair value of nonvested awards on equity-based plans excluding option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, revenue or profit achievement stock award plan) for which the employer is contingently obligated to issue equity instruments or transfer assets to an employee who has not yet satisfied service or performance criteria necessary to gain title to proceeds from the sale of the award or underlying shares or units.

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- Definition

The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan 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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