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Schedule II - Valuation and Qualifying Accounts (Detail) - USD ($)
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Inventory Reserve [Member]      
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]      
Charged (credited) to expenses $ 0 $ 0 $ 0
Accounts Receivable Reserve [Member]      
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]      
Balance at beginning of year   2,345,729 2,315,797
Charged (credited) to expenses $ 0 0 0
Charged (credited) to other accounts     29,932
Deductions   $ (2,345,729)  
Balance at ending of year     $ 2,345,729