Annual report pursuant to Section 13 and 15(d)

Income Taxes -Summary of Valuation Allowance (Detail)

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Income Taxes -Summary of Valuation Allowance (Detail) - USD ($)
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Income Tax Disclosure [Abstract]    
January 1, $ 46,171,964 $ 39,719,606
Increase in valuation allowance 17,177,323 6,452,358
December 31, $ 63,349,287 $ 46,171,964