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Fair Value Measurements - Summary of Changes in Fair Value of Company's Level 3 Financial Instruments (Detail) - USD ($) | 1 Months Ended | 3 Months Ended | 9 Months Ended
--- | --- | --- | ---
Mar. 31, 2016 | Sep. 30, 2016 | Sep. 30, 2015 | Sep. 30, 2016 | Sep. 30, 2015
Fair Value Liabilities Measured On Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Financial liabilities, beginning balance |  |  |  | $ 2,123,000 |
Change in fair value upon revaluation |  |  |  | (4,194,000) | $ (233,000)
Change in fair value upon revaluation |  | $ 0 | $ 805,000 | (525,000) | $ 659,000
Settlement of redeemable convertible preferred stock tranche liability due to the issuance of Series C redeemable convertible preferred stock | $ (5,800,000) |  |  | (5,837,000) |
Reclassification of redeemable convertible preferred stock warrant liability to redeemable convertible preferred stock |  |  |  | (1,005,000) |
Redeemable Convertible Preferred Stock Tranche Liability [Member] |  |  |  |  |
Fair Value Liabilities Measured On Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Financial liabilities, beginning balance |  |  |  | 1,643,000 |
Redeemable Convertible Preferred Stock Warrant Liability [Member] |  |  |  |  |
Fair Value Liabilities Measured On Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Financial liabilities, beginning balance |  |  |  | 480,000 |
Reclassification of redeemable convertible preferred stock warrant liability to redeemable convertible preferred stock |  |  |  | (1,000,000) |
Level 3 [Member] |  |  |  |  |
Fair Value Liabilities Measured On Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Financial liabilities, beginning balance |  |  |  | 2,123,000 |
Level 3 [Member] | Redeemable Convertible Preferred Stock Tranche Liability [Member] |  |  |  |  |
Fair Value Liabilities Measured On Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Financial liabilities, beginning balance |  |  |  | 1,643,000 |
Change in fair value upon revaluation |  |  |  | 4,194,000 |
Settlement of redeemable convertible preferred stock tranche liability due to the issuance of Series C redeemable convertible preferred stock |  |  |  | (5,837,000) |
Level 3 [Member] | Redeemable Convertible Preferred Stock Warrant Liability [Member] |  |  |  |  |
Fair Value Liabilities Measured On Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Financial liabilities, beginning balance |  |  |  | 480,000 |
Change in fair value upon revaluation |  |  |  | 525,000 |
Reclassification of redeemable convertible preferred stock warrant liability to redeemable convertible preferred stock |  |  |  | $ (1,005,000) |

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