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Long-Term Debt - Summary of Long Term Debt (Detail) - USD ($) $ in Thousands | Sep. 30, 2021 | Dec. 31, 2020
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Debt Disclosure [Abstract] |  |
Principal amount of long-term debt | $ 32,500 | $ 32,500
Debt discount, net of accretion | 266 | 223
Cumulative accretion of end of term payments | 970 | 455
Long-term debt | 33,736 | 33,178
Current portion of long-term debt | (693) | 0
Long-term debt, net of current portion | $ 33,043 | $ 33,178

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