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Common Stock - Additional Information (Detail) $ / shares in Units, $ in Millions |  |  |  | 3 Months Ended |
--- | --- | --- | --- | --- | ---
Sep. 11, 2018 $ / shares shares | Aug. 14, 2018 USD ($) $ / shares shares | Aug. 08, 2018 shares | Dec. 31, 2018 USD ($) $ / shares shares | Sep. 30, 2018 $ / shares shares
Class of Warrant or Right [Line Items] |  |  |  |  |
Warrants term |  |  |  | 5 years |
Warrants of common stock exercise price | $ / shares |  |  |  | $ 0.004 |
Maximum percentage of stock pertaining to restrictions |  |  |  | 24.90% |
Extended term of outstanding warrants expiration period |  |  |  | 5 years |
Warrants of common stock expiration date |  |  |  | Sep. 30, 2023 |
Warrants to purchase shares of common stock |  |  |  | 250,000 |
Common stock, stock split |  |  |  | Effected a 2.5-for-1 stock split |
Stock split ratio |  |  | 2.5 |  |
Common stock, shares authorized |  |  | 125,000,000 | 125,000,000 | 125,000,000
Preferred stock, shares authorized |  |  | 5,000,000 | 5,000,000 | 5,000,000
Stock issued during period, shares, new issues | 1,344,500 |  |  |  |
Common stock, no par value | $ / shares |  |  |  | $ 0 | $ 0
Common stock, warrants issued |  |  |  | 10,614,990 | 10,614,990
IPO [Member] |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |
Stock issued during period, shares, new issues |  | 9,630,000 |  |  |
Common stock, no par value | $ / shares |  |  |  |  |
Shares issued, price per share | $ / shares |  | $ 12.00 |  |  |
Gross proceeds of initial public offering | $ |  | $ 115.6 |  | $ 124.2 |
Net proceeds from initial public offering | $ |  |  |  | 111.7 |
Underwriting discounts and commissions | $ |  |  |  | 8.7 |
Offering costs | $ |  |  |  | $ 3.8 |
Underwriter Options [Member] |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |
Common stock, warrants issued |  | 1,444,500 |  |  |
Purchased Directly From Company [Member] |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |
Stock issued during period, shares, new issues | 723,985 |  |  |  |
Purchased Directly From Selling Shareholders [Member] |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |
Stock issued during period, shares, new issues | 620,515 |  |  |  |
Firm Shares and Option Shares [Member] |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |
Shares issued, price per share | $ / shares | $ 12.00 |  |  |  |

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