Annual report pursuant to Section 13 and 15(d)

Income taxes (Details) - Benefit (provision) for income taxes were at rates different from U.S. federal statutory rates

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Income taxes (Details) - Benefit (provision) for income taxes were at rates different from U.S. federal statutory rates
5 Months Ended 7 Months Ended 12 Months Ended
Dec. 31, 2017
Jul. 31, 2018
Jul. 31, 2019
Jul. 31, 2018
Jul. 31, 2017
Benefit (provision) for income taxes were at rates different from U.S. federal statutory rates [Abstract]          
Federal statutory rate 34.00% 21.00% (21.00%) 26.40% 34.00%
Compensation and other expenses not deductible for income tax return purposes     (15.30%) (1.00%) (14.50%)
Change in valuation allowance     36.30% 73.90% 64.00%
State tax law change         (81.10%)
Impact of Tax Act on valuation allowance       (100.10%)  
AMT refund under Tax Act       9.60%  
Other       0.80% (2.40%)
      9.60%