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. 29, 2018	Sep. 30, 2017	Sep. 29, 2018	Sep. 30, 2017
Stock Options
Weighted-average assumptions
Weighted-average fair value of grants per share	$ 1.81	$ 3.89	$ 1.98	$ 4.54
Expected volatility	44.10%	42.10%	43.83%	40.54%
Risk-free interest rate	2.87%	1.84%	2.58%	1.77%
Expected term of options (in years)	3 years 10 months 24 days	4 years 29 days	4 years 4 months 28 days	4 years 1 month 6 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	$ 1.87	$ 2.76	$ 2.24	$ 2.75
Expected volatility	50.64%	48.59%	47.64%	43.51%
Risk-free interest rate	2.58%	1.36%	2.01%	1.22%
Expected term of options (in years)	1 year 6 months 29 days	6 months	1 year 3 months 29 days	7 months 24 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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (f)(2)(i)
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-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 14.D.2)
-URI http://asc.fasb.org/extlink&oid=115993241&loc=d3e301413-122809

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