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Shares Underlying Stock Options, Excluded from Calculation of Weighted Average Number of Shares Outstanding used for Calculation of Diluted Net Loss Per Share (Detail) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted average number of anti-dilutive potential shares	18,619	16,211	13,686
Stock Options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted average number of anti-dilutive potential shares	17,373	15,592	13,681
Restricted Stock Units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted average number of anti-dilutive potential shares	1,225	576
Employee Stock Purchase Plan Rights
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted average number of anti-dilutive potential shares	21	43	5

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- Definition

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257

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- Definition

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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