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Redeemable Convertible Preferred Stock Tranche Liability - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands |  | 1 Months Ended | 3 Months Ended | 9 Months Ended | 12 Months Ended |
--- | --- | --- | --- | --- | --- | ---
Jul. 10, 2015 | Mar. 31, 2016 | Sep. 30, 2016 | Sep. 30, 2016 | Sep. 30, 2015 | Dec. 31, 2015 | Jul. 31, 2015
Temporary Equity [Line Items] |  |  |  |  |  |  |
Redeemable convertible preferred stock, shares issued |  |  | 0 | 0 |  | 77,185,117 |
Redeemable convertible preferred stock, proceeds |  |  |  | $ 22,508 | $ 17,362 |  |
Fair value of redeemable convertible preferred stock liability reclassified |  | $ 5,800 |  | 5,837 |  |  |
Change in fair value of redeemable convertible preferred stock tranche liabilities |  |  |  | 4,194 | $ 233 |  |
Second Tranche Warrants [Member] |  |  |  |  |  |  |
Temporary Equity [Line Items] |  |  |  |  |  |  |
Probability of exercisability percentage |  |  |  |  |  | 0.00% |
Series C Redeemable Convertible Preferred Stock [Member] |  |  |  |  |  |  |
Temporary Equity [Line Items] |  |  |  |  |  |  |
Redeemable convertible preferred stock, shares issued |  | 45,189,794 |  |  |  |  |
Redeemable convertible preferred stock, price per share |  |  |  |  |  | $ 0.4979 | $ 0.4979
Redeemable convertible preferred stock, proceeds | $ 17,500 | $ 22,500 |  |  |  |  |
Fair value of redeemable convertible preferred stock liability | $ 1,000 | $ 5,800 |  |  |  | $ 1,600 |
Probability of exercisability percentage | 90.00% |  |  |  |  | 95.00% |
Fair value assumptions, expected term | 1 year | 2 years |  |  |  | 6 months 11 days |
Fair value assumptions, risk-free interest rate | 0.50% | 0.73% |  |  |  | 0.90% |
Fair value assumptions, expected volatility |  | 52.00% |  |  |  |  |
Change in fair value of redeemable convertible preferred stock tranche liabilities |  |  | $ 0 | $ 4,200 |  |  |
Series C Redeemable Convertible Preferred Stock [Member] | Second Tranche Warrants [Member] |  |  |  |  |  |  |
Temporary Equity [Line Items] |  |  |  |  |  |  |
Additional shares to be issued upon the achievement of certain development milestones | 45,189,794 |  |  |  |  |  |
Series C Redeemable Convertible Preferred Stock [Member] | Option Pricing Model [Member] |  |  |  |  |  |  |
Temporary Equity [Line Items] |  |  |  |  |  |  |
Fair value assumptions, weighted volatility rate |  | 67.00% |  |  |  |  |
Series C Redeemable Convertible Preferred Stock [Member] | PWERM [Member] |  |  |  |  |  |  |
Temporary Equity [Line Items] |  |  |  |  |  |  |
Fair value assumptions, weighted volatility rate |  | 33.00% |  |  |  |  |
Maximum [Member] | Series C Redeemable Convertible Preferred Stock [Member] |  |  |  |  |  |  |
Temporary Equity [Line Items] |  |  |  |  |  |  |
Redeemable convertible preferred stock, shares issued | 35,147,617 |  |  |  |  |  | 80,337,411

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- Definition The number of securities classified as temporary equity that have been sold (or granted) to the entity's shareholders. Securities issued include securities outstanding and securities held in treasury. Temporary equity is a security with redemption features that are outside the control of the issuer, is not classified as an asset or liability in conformity with GAAP, and is not mandatorily redeemable. Includes any type of security that is redeemable at a fixed or determinable price or on a fixed or determinable date or dates, is redeemable at the option of the holder, or has conditions for redemption which are not solely within the control of the issuer. If convertible, the issuer does not control the actions or events necessary to issue the maximum number of shares that could be required to be delivered under the conversion option if the holder exercises the option to convert the stock to another class of equity. If the security is a warrant or a rights issue, the warrant or rights issue is considered to be temporary equity if the issuer cannot demonstrate that it would be able to deliver upon the exercise of the option by the holder in all cases. Includes stock with put option held by ESOP and stock redeemable by holder only in the event of a change in control of the issuer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(27)(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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