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Fair Value-Based Measurements and Weighted-Average Assumptions (Detail) - $ / shares	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted-average fair value			$ 9.18	$ 7.40
Risk-free interest rate			0.40%	0.20%
Expected life (in years)			1 year 2 months 12 days	1 year 2 months 12 days
Volatility			0.60%	0.90%
Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted-average fair value	$ 17.63	$ 10.10	$ 13.23	$ 15.20
Risk-free interest rate	1.70%	1.90%	1.70%	1.80%
Expected life (in years)	5 years 9 months 18 days	5 years 6 months	5 years 10 months 24 days	5 years 10 months 24 days
Volatility	0.70%	0.80%	0.70%	1.40%

X

- 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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef



-Publisher FASB



-Name Accounting Standards Codification



-Topic 718



-SubTopic 10



-Section 50



-Paragraph 2



-Subparagraph (f)(2)(ii)



-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef



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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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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

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

Reference 1: http://www.xbrl.org/2003/role/presentationRef



-Publisher FASB



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