Equity Plans and Stock-Based Compensation - Option Activity under Stock-Based Compensation Plans (Detail) $ / shares in Units, shares in Thousands, $ in Thousands	9 Months Ended
Sep. 30, 2019 USD ($) $ / shares shares
Shares Underlying Outstanding Options
Beginning balance \| shares	5,750
Options granted \| shares	3,025
Options exercised \| shares	(10)
Ending balance \| shares	7,997
Vested and expected to vest at September 30, 2019 \| shares	7,692
Exercisable at September 30, 2019 \| shares	4,485
Weighted-Average Exercise Price Per Share
Beginning balance \| $ / shares	$ 18.20
Options granted \| $ / shares	6.94
Options exercised \| $ / shares	5.75
Ending balance \| $ / shares	14.43
Vested and expected to vest at September 30, 2019 \| $ / shares	14.70
Exercisable at September 30, 2019 \| $ / shares	$ 18.40
Weighted-Average Remaining Contractual Term (years)
Balance at September 30, 2019	4 years 6 months 25 days
Vested and expected to vest at September 30, 2019	4 years 6 months 3 days
Exercisable at September 30, 2019	3 years 6 months 25 days
Aggregate Intrinsic Value
Balance at September 30, 2019 \| $	$ 6
Vested and expected to vest at September 30, 2019 \| $	$ 5
Unvested
Shares Underlying Outstanding Options
Options cancelled \| shares	(632)
Weighted-Average Exercise Price Per Share
Options cancelled \| $ / shares	$ 12.53
Vested
Shares Underlying Outstanding Options
Options cancelled \| shares	(136)
Weighted-Average Exercise Price Per Share
Options cancelled \| $ / shares	$ 16.77

Share based compensation arrangement by share based payment award options aggregate intrinsic value.

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Share based compensation arrangement by share based payment award options weighted average remaining contractual term.

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The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.

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Number of options or other stock instruments for which the right to exercise has lapsed under the terms of the plan agreements.

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The number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan.

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Gross number of share options (or share units) granted during the period.

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Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

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Number of options outstanding, including both vested and non-vested options.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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Weighted-average exercise price, at which grantee can acquire shares reserved for issuance, for fully vested and expected to vest exercisable or convertible options. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Amount by which current fair value of underlying stock exceeds exercise price of fully vested and expected to vest options outstanding. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Number of fully vested and expected to vest options outstanding that can be converted into shares under option plan. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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Weighted average price at which grantees could have acquired the underlying shares with respect to stock options of the plan that expired.

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Weighted average price at which grantees could have acquired the underlying shares with respect to stock options that were terminated.

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Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

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Weighted average remaining contractual term for vested portions of options outstanding and currently exercisable or convertible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Weighted average remaining contractual term for fully vested and expected to vest options outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Number of share options (or share units) exercised during the current period.

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