Financial Assets Measured at Fair Value on Recurring Basis and Classified by Fair Value Hierarchy (Detail) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	Jan. 31, 2017	Jul. 31, 2016
Marketable equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	$ 11,029	$ 4,209
Marketable corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring		12,559
Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	86,898	101,224
Fair Value, Inputs, Level 1 | Marketable equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	11,029	4,209
Fair Value, Inputs, Level 1 | Marketable corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring		12,559
Fair Value, Inputs, Level 1 | Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	$ 86,898	$ 101,224