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Convertible Preferred Stock and Stockholders' Equity - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands |  | 1 Months Ended | 3 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | --- | --- | ---
Oct. 23, 2017 | Jan. 31, 2019 | Dec. 31, 2018 | Mar. 31, 2019 | Dec. 31, 2018 | Nov. 02, 2018 | Nov. 01, 2018
Class Of Stock [Line Items] |  |  |  |  |  |  |
Authorized capital stock | 33,853,333 |  |  |  |  |  |
Common stock, shares authorized | 18,666,666 |  | 100,000,000 | 100,000,000 | 100,000,000 | 100,000,000 |
Capital stock par value | $ 0.001 |  |  |  |  | $ 0.001 |
Convertible preferred stock |  |  |  |  |  | 5,000,000 |
Dividends, value | $ 6,539 |  |  |  |  |  |
Dividends, fair value |  |  |  |  |  |  | $ 10,152
Preferred shares converted into common stock |  |  |  |  |  |  | 13,277,864
Preferred stock, shares issued |  |  |  | 0 |  |  |
Proceeds from issuance of common stock, net of costs |  |  |  | $ 1,604 |  |  |
Securities Purchase Agreement |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |
Common stock, number of shares available for sale |  |  |  |  |  | 2,089,136 |
Proceeds from issuance of common stock, net of costs |  | $ 1,634 | $ 8,295 |  |  |  |
Issuance cost |  |  |  |  | $ 831 |  |
Common Stock |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |
Shares issued and sold |  |  |  | 227,628 |  |  |
Common Stock | Securities Purchase Agreement |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |
Shares issued and sold |  | 227,628 |  |  | 1,270,905 |  |
Common stock, shares issued price per share |  |  | $ 7.18 |  | $ 7.18 |  |
Convertible Preferred Stock |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |
Convertible preferred stock | 15,186,664 |  |  |  |  |  |
Series A-3 Convertible Preferred Stock |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |
Convertible preferred stock | 1,266,666 |  |  |  |  |  |
Series A-2 Convertible Preferred Stock |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |
Convertible preferred stock | 1,186,666 |  |  |  |  |  |
Number of shares issued as dividends |  |  |  |  | 49,456 |  |
Series A-1 Convertible Preferred Stock [Member] |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |
Convertible preferred stock | 1,733,333 |  |  |  |  |  |
Number of shares issued as dividends |  |  |  |  | 66,255 |  |
Series A Convertible Preferred Stock |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |
Convertible preferred stock | 9,333,333 |  |  |  |  |  |
Number of shares issued as dividends |  |  |  |  | 944,694 |  |
Series B Convertible Preferred Stock |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |
Convertible preferred stock | 1,666,666 |  |  |  |  |  |

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