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Black-Scholes Valuation Model and Weighted-Average Assumptions (Detail) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average fair value per share, other than options			$ 4.23
Expected dividends			0.00%	0.00%
Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average fair value per share, options	$ 3.42	$ 2.36	$ 3.30	$ 2.76
Risk-free interest rate	0.50%	1.00%	0.50%	1.60%
Expected life (in years)	4 years	4 years	4 years	4 years
Volatility	1.50%	1.60%	1.60%	1.60%
Expected dividends
Employee stock purchase plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average fair value per share, other than options			$ 2.85	$ 2.19
Risk-free interest rate			0.20%	0.30%
Expected life (in years)			1 year 2 months 12 days	1 year 2 months 12 days
Volatility			1.50%	1.60%
Expected dividends

X

- 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).

+ References

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(2)(iii)(1)

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X

- Definition

The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

+ References

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- Definition

Expected term of share-based compensation awards, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

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- Definition

The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

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The risk-free interest rate assumption that is used in valuing an option on its own shares.

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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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