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SIGNIFICANT ACCOUNTING POLICIES - Value added taxes (Details)
4 Months Ended 8 Months Ended 12 Months Ended
Apr. 30, 2018
Dec. 31, 2018
Dec. 31, 2018
SIGNIFICANT ACCOUNTING POLICIES      
Value added tax rate on gross sales (in percent) 17.00% 16.00%  
Value added tax rate for general VAT payer (in percent)     6.00%
Value added tax rate for small scale VAT payer (in percent)     3.00%