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Potential Shares, Excluded from Calculation of Weighted Average Number of Shares Outstanding used for Calculation of Diluted Net Loss Per Share (Detail) - shares shares in Thousands | 3 Months Ended | 9 Months Ended
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Sep. 30, 2018 | Sep. 30, 2017 | Sep. 30, 2018 | Sep. 30, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] |  |  |  |
Weighted average number of anti-dilutive potential shares | 19,874 | 18,942 | 20,004 | 18,646
Stock Options |  |  |  |
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] |  |  |  |
Weighted average number of anti-dilutive potential shares | 17,882 | 17,629 | 18,137 | 17,424
Restricted Stock Units |  |  |  |
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] |  |  |  |
Weighted average number of anti-dilutive potential shares | 1,989 | 1,313 | 1,865 | 1,211
Employee Stock Purchase Plan Rights |  |  |  |
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] |  |  |  |
Weighted average number of anti-dilutive potential shares | 3 |  | 2 | 11

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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://fasb.org/us-gaap/role/ref/legacyRef -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 + Details
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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. + Details
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