Employee Defined Contribution Plan - Additional Information (Details) - USD ($) |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
|
| Compensation And Retirement Disclosure [Abstract] | |||
| Employee benefits, expense | $ 579,094 | $ 288,666 | $ 79,878 |