Income taxes (Details) - Benefit (provision) for income taxes were at rates different from U.S. federal statutory rates	12 Months Ended
	Jul. 31, 2014	Jul. 31, 2013	Jul. 31, 2012
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	(6.60%)	(0.90%)	(0.50%)
State income taxes, net of benefit of federal tax deduction	0.20%	2.50%	0.90%
Change in valuation allowance	(16.50%)	(32.70%)	(23.20%)
Impairment of goodwill			(7.10%)
State tax law change	(12.30%)
Other	0.50%	0.90%	(0.10%)
	(0.70%)	3.80%	4.00%