Income taxes (Details) - USD ($)	5 Months Ended	7 Months Ended	12 Months Ended
	Dec. 31, 2017	Jul. 31, 2018	Jul. 31, 2019	Jul. 31, 2018	Jul. 31, 2017
Income taxes (Details) [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	34.00%	21.00%	(21.00%)	26.40%	34.00%
Tax Cut and Job Act 2017 Deferred Tax Assets Valuation Allowance			$ 0	$ 11,500,000
Effective Income Tax Rate Reconciliation, Tax Credit, Amount			0	1,100,000
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount			(900,000)	8,100,000
Deferred Tax Assets, Operating Loss Carryforwards, Subject to Expiration			59,100,000
Deferred Tax Assets Research and Development and Other Tax Credit Carryforwards		$ 1,286,000	1,350,000	$ 1,286,000
Deferred Tax Assets, Operating Loss Carryforwards			2,700,000
Foreign Loss Carryforwards			15,400,000
Liability for Uncertain Tax Position			0
U.S. Federal Tax [Member]
Income taxes (Details) [Line Items]
Deferred Tax Assets Research and Development and Other Tax Credit Carryforwards			$ 1,300,000
Maximum [Member]
Income taxes (Details) [Line Items]
Operating Loss Carryforward Expiration Year End			2038
Maximum [Member] | Domestic Tax Authority [Member]
Income taxes (Details) [Line Items]
Operating Loss Carryforwards Expiration Year			2030
Maximum [Member] | Research Tax Credit Carryforward [Member]
Income taxes (Details) [Line Items]
Tax Credit Carryforward Expiration Year			2039
Minimum [Member]
Income taxes (Details) [Line Items]
Operating Loss Carryforward Expiration Year Begining			2037
Minimum [Member] | Domestic Tax Authority [Member]
Income taxes (Details) [Line Items]
Operating Loss Carryforwards Expiration Year			2038
Minimum [Member] | Research Tax Credit Carryforward [Member]
Income taxes (Details) [Line Items]
Tax Credit Carryforward Expiration Year			2025