Notes Payable to Investors - Additional Information (Detail) - USD ($) |
1 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
Feb. 28, 2017 |
Oct. 31, 2016 |
Sep. 30, 2018 |
Dec. 31, 2016 |
|
| Convertible Note Financing [Member] | ||||
| Debt Instrument [Line Items] | ||||
| Convertible notes payable | $ 9,000,000 | |||
| Debt instrument, accrued interest rate | 8.00% | |||
| Gross proceeds from sale of capital stock | $ 30,000,000 | |||
| Additional Convertible Note Financings [Member] | ||||
| Debt Instrument [Line Items] | ||||
| Convertible notes payable | $ 300,000 | $ 3,500,000 | ||
| Maturity date | Mar. 31, 2017 | Mar. 31, 2017 | ||
| Debt issuance cost | $ 125,935 | $ 125,935 | ||