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Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Jan. 01, 2019
Jun. 05, 2018
Sep. 15, 2017
Dec. 31, 2016
Warrant liability   $ 2,679,633   $ 4,194,408    
Change in fair value of warrants $ 1,514,775 465,633        
Exercise of warrants liability 4,194,408          
Impairment charges 0 0        
Liability for uncertainty in income taxes 0 $ 0        
Unrecognized tax benefits, income tax penalties and interest accrued $ 0          
Statutory tax rate 19.00% 19.25%        
Minimum [Member] | Subsequent Event [Member]            
Discount rate     8.00%      
Operating lease right-of-use asset     $ 3,300,000      
Operating lease liability     $ 3,600,000      
Maximum [Member] | Subsequent Event [Member]            
Discount rate     10.00%      
Operating lease right-of-use asset     $ 3,600,000      
Operating lease liability     $ 3,800,000      
Valuation Technique, Option Pricing Model [Member]            
Pricing valuation of ordinary share   $ 5.63     $ 2.64 $ 7.57
Federal [Member]            
Statutory tax rate 21.00% 34.00%        
Capital in Excess of Nominal Value [Member]            
Exercise of warrants liability $ 4,194,408