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, 2018
Jul. 31, 2017
Jul. 31, 2016
Benefit (provision) for income taxes were at rates different from U.S. federal statutory rates [Abstract]          
Federal statutory rate 35.00% 21.00% 26.40% 34.00% (34.00%)
Penalties and other expenses not deductible for income tax return purposes     (1.00%) (14.50%) (1.10%)
State income taxes, net of benefit of federal tax deduction         (0.10%)
Change in valuation allowance     73.90% 64.00% 32.90%
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%   (2.30%)