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Stockholders' Equity - Additional Information (Detail) - USD ($) |  |  | 1 Months Ended | 12 Months Ended
--- | --- | --- | --- | ---
Dec. 11, 2020 | Jan. 08, 2018 | Jan. 31, 2020 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Stockholders Equity Note [Line Items] |  |  |  |  |  |
Common stock, shares issued and sold |  |  |  | 168,170,000 | 144,291,000 |
Common stock, par value |  |  |  | $ 0.001 | $ 0.001 |
Net proceeds from public offering |  |  |  | $ 76,534,000 | $ 26,931,000 | $ 85,036,000
Common Stock |  |  |  |  |  |
Stockholders Equity Note [Line Items] |  |  |  |  |  |
Common stock, number of shares issued |  |  |  | 19,338,000 | 5,648,000 | 18,202,000
Underwritten Public Offering | Common Stock |  |  |  |  |  |
Stockholders Equity Note [Line Items] |  |  |  |  |  |
Common stock, shares issued and sold |  |  | 16,866,667 |  |  |
Common stock, par value |  |  | $ 0.001 |  |  |
Common stock, sale of stock, price per share |  |  | $ 3.75 |  |  |
Net proceeds from public offering |  |  | $ 62,700,000 |  |  |
Amendment No. 3 | Cantor Fitzgerald & Co | Sales Agreements |  |  |  |  |  |
Stockholders Equity Note [Line Items] |  |  |  |  |  |
Net proceeds from public offering |  |  |  | $ 13,900,000 |  |
Percentage of proceeds payable as compensation to underwriter |  | 2.00% |  |  |  |
Common stock, number of shares issued |  |  |  | 2,500,000 |  |
Amendment No. 3 | Cantor Fitzgerald & Co. and Stifel, Nicolaus & Company, Incorporated | Sales Agreements |  |  |  |  |  |
Stockholders Equity Note [Line Items] |  |  |  |  |  |
Percentage of proceeds payable as compensation to underwriter | 2.00% |  |  |  |  |
Common stock, number of shares issued |  |  |  | 0 |  |
Maximum common stock offering price | $ 100,000,000.0 |  |  |  |  |

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