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Preferred Stock Warrants - Additional Information (Detail) | 1 Months Ended | 3 Months Ended | 9 Months Ended | 12 Months Ended |  |
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Jul. 31, 2016 IPO | Apr. 30, 2016 USD ($) shares | Aug. 31, 2013 $ / shares shares | Sep. 30, 2016 USD ($) shares | Sep. 30, 2015 USD ($) | Sep. 30, 2016 USD ($) shares | Sep. 30, 2015 USD ($) | Dec. 31, 2015 USD ($) shares | May 31, 2016 shares | Mar. 31, 2016 shares
Class of Warrant or Right [Line Items] |  |  |  |  |  |  |  |  |  |
Redeemable convertible preferred stock, shares issued | shares |  |  |  | 0 |  | 0 |  | 77,185,117 |  |
Redeemable convertible preferred stock, shares outstanding | shares |  |  |  | 0 |  | 0 |  | 77,185,117 |  |
Proceeds from issuance of redeemable convertible preferred stock upon exercise of warrants | $ |  |  |  |  |  | $ 22,508,000 | $ 17,362,000 |  |  |
Remeasured fair value of warrants | $ |  | $ 1,000,000 |  |  |  |  |  |  |  |
Reclassification of redeemable convertible preferred stock warrant liability to redeemable convertible preferred stock | $ |  |  |  |  |  | 1,005,000 |  |  |  |
Change in fair value of redeemable convertible preferred stock warrant liability | $ |  |  |  | $ 0 | $ (805,000) | 525,000 | $ (659,000) |  |  |
Redeemable Convertible Preferred Stock Warrant Liability [Member] |  |  |  |  |  |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |  |  |  |  |  |
Reclassification of redeemable convertible preferred stock warrant liability to redeemable convertible preferred stock | $ |  |  |  |  |  | $ 1,000,000 |  |  |  |
Option Pricing Model [Member] |  |  |  |  |  |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |  |  |  |  |  |
Percentage of weighted value per share |  | 67.00% |  |  |  |  |  |  |  |
PWERM [Member] |  |  |  |  |  |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |  |  |  |  |  |
Percentage of weighted value per share |  | 33.00% |  |  |  |  |  |  |  |
Fair value assumptions probabilities, number of IPO scenarios | IPO | 3 |  |  |  |  |  |  |  |  |
First Tranche Warrants [Member] |  |  |  |  |  |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |  |  |  |  |  |
Number of convertible preferred stock issued upon exercise of stock warrants | shares |  |  | 2,000,000 |  |  |  |  |  |  |
Second Tranche Warrants [Member] |  |  |  |  |  |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |  |  |  |  |  |
Warrants issued date |  |  |  |  |  | Aug. 15, 2014 |  |  |  |
Preferred Stock Warrant Liability [Member] |  |  |  |  |  |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |  |  |  |  |  |
Warrants outstanding, fair value | $ |  |  |  |  |  |  |  | $ 480,000 |  |
Risk-free interest rate |  | 0.73% |  |  |  |  |  | 0.90% |  |
Expected life |  | 2 years |  |  |  |  |  | 1 year 7 months 6 days |  |
Expected volatility |  | 52.00% |  |  |  |  |  | 57.00% |  |
First Tranche Warrants [Member] |  |  |  |  |  |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |  |  |  |  |  |
Probability of exercisability percentage |  |  |  |  |  |  |  | 95.00% |  |
Second Tranche Warrants [Member] |  |  |  |  |  |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |  |  |  |  |  |
Probability of exercisability percentage |  |  |  |  |  |  |  | 0.00% |  |
Series B Redeemable Convertible Preferred Stock [Member] |  |  |  |  |  |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |  |  |  |  |  |
Number of convertible preferred stock issued upon exercise of stock warrants | shares |  |  | 4,000,000 |  |  |  |  |  |  |
Warrants exercise price | $ / shares |  |  | $ 0.01 |  |  |  |  |  |  |
Percentage of warrants exercisable upon new product announcement |  |  | 50.00% |  |  |  |  |  |  |
Redeemable convertible preferred stock, shares issued | shares |  | 1,999,998 |  |  |  |  |  |  |  |
Redeemable convertible preferred stock, shares outstanding | shares |  |  |  |  |  |  |  |  |  | 2,000,000
Proceeds from issuance of redeemable convertible preferred stock upon exercise of warrants | $ |  | $ 20,000 |  |  |  |  |  |  |  |
Number of redeemable convertible preferred stock expired unexercised | shares |  |  |  |  |  |  |  |  | 2,000,000 |

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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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