Financial Assets and Liabilities Measured at Fair Value and Related Valuation Inputs (Detail) (USD $) In Thousands, unless otherwise specified	Jan. 31, 2015		Jul. 31, 2014
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, Fair Value Disclosure	$ 130,309		$ 98,928
Fair Value, Inputs, Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, Fair Value Disclosure	79,245		63,243
Fair Value, Inputs, Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, Fair Value Disclosure	51,064		35,685
Cash and Cash Equivalents
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, Fair Value Disclosure	73,419	[1]	59,269	[1]
Cash and Cash Equivalents | Fair Value, Inputs, Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, Fair Value Disclosure	73,419	[1]	59,269	[1]
Marketable Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, Fair Value Disclosure	56,890		39,659
Marketable Securities | Fair Value, Inputs, Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, Fair Value Disclosure	5,826		3,974
Marketable Securities | Fair Value, Inputs, Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, Fair Value Disclosure	$ 51,064		$ 35,685

[1] Cash and cash equivalents as of January 31, 2015 and July 31, 2014 included cash held in operating accounts of approximately $71.3 million and $56.0 million, respectively that are not subject to fair value measurements. For purposes of this disclosure, they are included as having level 1 inputs.