Weighted-Average Fair Value of Stock Options and Employee Stock Purchase Rights using Weighted-Average Assumptions (Detail) - $ / shares	3 Months Ended	9 Months Ended
Sep. 30, 2017	Oct. 01, 2016	Sep. 30, 2017	Oct. 01, 2016
Stock Options
Weighted-average assumptions
Weighted-average fair value of grants per share	$ 3.89	$ 1.90	$ 4.54	$ 1.75
Expected volatility	42.10%	40.53%	40.54%	44.00%
Risk free interest rate	1.84%	0.97%	1.77%	0.94%
Expected term of options (in years)	4 years 29 days	3 years 11 months 15 days	4 years 1 month 6 days	4 years 3 months 15 days
Dividend yield	0.00%	0.00%	0.00%	0.00%
Stock Purchase Rights
Weighted-average assumptions
Weighted-average fair value of grants per share	$ 2.76	$ 1.69	$ 2.75	$ 1.55
Expected volatility	48.59%	37.51%	43.51%	39.22%
Risk free interest rate	1.36%	0.63%	1.22%	0.75%
Expected term of options (in years)	6 months	1 year	7 months 24 days	1 year 10 months 14 days
Dividend yield	0.00%	0.00%	0.00%	0.00%

No definition available.

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- 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.

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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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- Definition

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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- 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
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (f)(2)(i)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 14.D.2)
-URI http://asc.fasb.org/extlink&oid=27013229&loc=d3e301413-122809

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