Stock-Based Compensation - Summary of Stock Option Activity (Detail)	3 Months Ended
Mar. 31, 2019 $ / shares shares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Shares Issuable Under Options, Beginning balance \| shares	4,435,000
Shares Issuable Under Options, Granted \| shares	638,000
Shares Issuable Under Options, Exercised \| shares	(118)
Shares Issuable Under Options, Cancelled \| shares	(92,000)
Shares Issuable Under Options, Ending balance \| shares	4,980,879
Shares Issuable Under Options, Options exercisable at March 31, 2019 \| shares	4,981,000
Shares Issuable Under Options, Options exercisable at March 31, 2019 \| shares	2,689,000
Weighted Average Exercise Price Per Share, Beginning balance \| $ / shares	$ 19.21
Weighted Average Exercise Price Per Share, Granted \| $ / shares	14.47
Weighted Average Exercise Price Per Share, Exercised \| $ / shares	7.15
Weighted Average Exercise Price Per Share, Cancelled \| $ / shares	21.85
Weighted Average Exercise Price Per Share, Ending balance \| $ / shares	18.56
Weighted Average Exercise Price Per Share, Options vested and expected to vest \| $ / shares	18.56
Weighted Average Exercise Price Per Share, Options exercisable \| $ / shares	$ 17.67

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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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For presentations that combine terminations, 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 or that expired.

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Weighted average price of options that were either forfeited or expired.

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

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

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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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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 exercise price, at which grantee can acquire shares reserved for issuance, for 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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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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

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