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Fair Value Measurements - Schedule of Assets and Liabilities Measured at Fair Value (Detail) - USD ($) $ in Thousands | Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014
--- | --- | --- | ---
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Total financial assets | $ 85,169 | $ 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 | 21,841 | 7,368 |
Governmental Bonds [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Total financial assets | 41,289 |  |
Money Market Funds [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Total financial assets | 11,270 | 2,136 |
Commercial Paper [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Total financial assets | 10,769 | 500 |
Level 1 [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Total financial assets | 11,270 | 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 | 11,270 | 2,136 |
Level 2 [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Total financial assets | 73,899 | 7,868 |
Level 2 [Member] | Corporate Bonds Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Total financial assets | 21,841 | 7,368 |
Level 2 [Member] | Governmental Bonds [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Total financial assets | 41,289 |  |
Level 2 [Member] | Commercial Paper [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Total financial assets | $ 10,769 | 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 | $ 1,023

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