Income taxes (Details) - Benefit (provision) for income taxes were at rates different from U.S. federal statutory rates	12 Months Ended
	Jul. 31, 2016	Jul. 31, 2015	Jul. 31, 2014
Benefit (provision) for income taxes were at rates different from U.S. federal statutory rates [Abstract]
Federal statutory rate	(34.00%)	34.00%	34.00%
Penalties and other expenses not deductible for income tax return purposes	(1.10%)	(18.60%)	(6.60%)
State income taxes, net of benefit of federal tax deduction	(0.40%)	(0.50%)	0.20%
Change in valuation allowance	32.90%	(15.20%)	(16.50%)
State tax law change			(12.30%)
Other		0.60%	0.50%
	(2.60%)	0.30%	(0.70%)