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Stockholders' Equity - Additional Information (Detail) - Cantor Fitzgerald & Co - Amendment No. 3 - Sales Agreement - USD ($) |  | 3 Months Ended
--- | --- | ---
Jan. 08, 2018 | Mar. 31, 2019
Stockholders Equity Note [Line Items] |  |
Maximum common stock offering price | $ 70,000,000 |
Percentage of proceeds payable as compensation to underwriter | 2.00% |
Unsold shares of common stock, value | $ 31,400,000 |
Common stock, number of shares issued |  | 0
Common stock registered for sale |  | $ 41,600,000

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