Stockholders' Equity - Summary of Stock Option Activity (Detail)	9 Months Ended
Sep. 30, 2017 $ / shares shares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Outstanding Options, Beginning Balance \| shares	4,014,988
Number of Outstanding Options, Granted \| shares	1,041,619
Number of Outstanding Options, Exercised \| shares	(32,221)
Number of Outstanding Options, Canceled/forfeited/expired \| shares	(327,971)
Number of Outstanding Options, Ending Balance \| shares	4,696,415
Weighted Average Exercise Price, Beginning Balance \| $ / shares	$ 6.73
Weighted Average Exercise Price, Granted \| $ / shares	3.27
Weighted Average Exercise Price, Exercised \| $ / shares	1.15
Weighted Average Exercise Price, Canceled/forfeited/expired \| $ / shares	6.99
Weighted Average Exercise Price, Ending Balance \| $ / shares	$ 5.98

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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.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iv)(3)-(4)
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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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- Definition

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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