Annual report pursuant to Section 13 and 15(d)

Income taxes (Details)

v3.20.2
Income taxes (Details) - USD ($)
$ in Millions
 12 Months Ended
Jul. 31, 2020
Jul. 31, 2019
Jul. 31, 2018
Dec. 31, 2017
Income taxes (Details) [Line Items]        
Deferred tax assets cumulative charges     $ 11.5  
Effective income tax rate reconciliation, cumulative tax benefit     $ 1.1  
Valuation allowance, deferred tax asset, increase (decrease), amount $ 6.6 $ (0.9)    
Deferred tax assets, operating loss carryforwards, subject to expiration 85.8      
Deferred tax assets, operating loss carryforward, not subject to expiration   $ 59.0    
Deferred tax assets, operating loss carryforwards, not subject to expiration 26.8      
Deferred tax assets research and development and other tax credit carryforwards 1.5      
Deferred tax assets, operating loss carryforwards 22.5      
Foreign loss carryforwards $ 15.5      
Maximum [Member]        
Income taxes (Details) [Line Items]        
Effective income tax rate reconciliation, at federal statutory income tax rate, percent       34.00%
Operating loss carryforward expiration year end 2038      
Minimum [Member]        
Income taxes (Details) [Line Items]        
Effective income tax rate reconciliation, at federal statutory income tax rate, percent       21.00%
Operating loss carryforward expiration year end 2030      
Research Tax Credit Carryforward [Member] | Maximum [Member]        
Income taxes (Details) [Line Items]        
Tax credit carryforward expiration year 2040      
Research Tax Credit Carryforward [Member] | Minimum [Member]        
Income taxes (Details) [Line Items]        
Tax credit carryforward expiration year 2025      
Domestic Tax Authority [Member] | Maximum [Member]        
Income taxes (Details) [Line Items]        
Operating loss carryforwards expiration year 2040      
Domestic Tax Authority [Member] | Minimum [Member]        
Income taxes (Details) [Line Items]        
Operating loss carryforwards expiration year 2038