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Fair Value Measurements - Summary of Changes in Fair Value of Company's Level 3 Financial Instruments (Detail) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014
Fair Value Liabilities Measured On Recurring and Nonrecurring Basis [Line Items] |  |  |
Financial liabilities, beginning balance | $ 2,123 |  |
Change in fair value upon revaluation | (525) | $ 543 | $ (872)
Change in fair value upon revaluation | (4,194) | (626) | (897)
Reclassification of redeemable convertible preferred stock warrant liability to redeemable convertible preferred stock | (1,005) |  |
Settlement of redeemable convertible preferred stock tranche liability due to the issuance of Series C redeemable convertible preferred stock | (5,837) |  |
Financial liabilities, ending balance |  | 2,123 |
Redeemable Convertible Preferred Stock Tranche Liability [Member] |  |  |
Fair Value Liabilities Measured On Recurring and Nonrecurring Basis [Line Items] |  |  |
Financial liabilities, beginning balance | 1,643 |  |
Financial liabilities, ending balance |  | 1,643 |
Redeemable Convertible Preferred Stock Warrant Liability [Member] |  |  |
Fair Value Liabilities Measured On Recurring and Nonrecurring Basis [Line Items] |  |  |
Financial liabilities, beginning balance | 480 |  |
Reclassification of redeemable convertible preferred stock warrant liability to redeemable convertible preferred stock | (1,000) |  |
Financial liabilities, ending balance |  | 480 |
Level 3 [Member] |  |  |
Fair Value Liabilities Measured On Recurring and Nonrecurring Basis [Line Items] |  |  |
Financial liabilities, beginning balance | 2,123 |  |
Financial liabilities, ending balance |  | 2,123 |
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 |  |
Issuance of Series C redeemable convertible preferred stock tranche liability |  | 1,017 |
Change in fair value upon revaluation | 4,194 | 626 |
Settlement of redeemable convertible preferred stock tranche liability due to the issuance of Series C redeemable convertible preferred stock | (5,837) |  |
Financial liabilities, ending balance |  | 1,643 |
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 | 1,023 |
Change in fair value upon revaluation | 525 | (543) |
Reclassification of redeemable convertible preferred stock warrant liability to redeemable convertible preferred stock | $ (1,005) |  |
Financial liabilities, ending balance |  | $ 480 | $ 1,023

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