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Fair Value Measurements - Schedule of Assets and Liabilities Measured at Fair Value (Detail) - USD ($) $ in Thousands | Sep. 30, 2016 | Dec. 31, 2015
--- | --- | ---
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total financial assets | $ 97,621 | $ 10,004
Total financial liabilities |  | 2,123
Redeemable Convertible Preferred Stock Tranche Liability [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total financial liabilities |  | 1,643
Redeemable Convertible Preferred Stock Warrant Liability [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total financial liabilities |  | 480
Corporate Bonds Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total financial assets | 600 | 7,368
Money Market Funds [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total financial assets | 95,122 | 2,136
Commercial Paper [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total financial assets | 1,899 | 500
Level 1 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total financial assets | 95,122 | 2,136
Level 1 [Member] | Money Market Funds [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total financial assets | 95,122 | 2,136
Level 2 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total financial assets | 2,499 | 7,868
Level 2 [Member] | Corporate Bonds Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total financial assets | 600 | 7,368
Level 2 [Member] | Commercial Paper [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total financial assets | $ 1,899 | 500
Level 3 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total financial liabilities |  | 2,123
Level 3 [Member] | Redeemable Convertible Preferred Stock Tranche Liability [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total financial liabilities |  | 1,643
Level 3 [Member] | Redeemable Convertible Preferred Stock Warrant Liability [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total financial liabilities |  | $ 480

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