Net income (loss) per share (Details) - shares	3 Months Ended		6 Months Ended
	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2018	Jan. 31, 2017
Weighted Average Stock Options [Member]
Net income (loss) per share (Details) [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount		888,000		804,000
Outstanding Options [Member]
Net income (loss) per share (Details) [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	0	494,000	0	247,000
In the Money Stock Options [Member] | Unvested Restricted Stock [Member]
Net income (loss) per share (Details) [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	719,000		825,000