Income Taxes - Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Jul. 31, 2018	Jul. 31, 2017	Jul. 31, 2016
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Expected statutory tax(1)	26.90%	35.00%	35.00%
Differential attributable to:
Foreign operations	0.60%	0.00%	0.60%
State and local taxes	3.70%	3.90%	3.20%
Domestic production deduction	(1.80%)	(2.70%)	(2.30%)
Acquisition-related items, net	0.00%	0.10%	0.00%
Impact of tax legislation on deferred taxes	(7.40%)	0.00%	0.00%
R&E tax credit	(0.70%)	(1.40%)	(1.10%)
Change in foreign tax rates	0.00%	0.00%	(0.40%)
Excess tax benefits	(1.70%)	(2.20%)	0.00%
Valuation allowance	2.40%	0.00%	0.00%
Other	0.50%	0.10%	1.20%
Consolidated effective tax rate (as a percent)	22.50%	32.80%	36.20%
Share-based compensation, excess tax benefit, amount	$ 2,173	$ 2,241