Financial Assets and Liabilities Measured at Fair Value and Related Valuation Inputs (Detail) (USD $) In Thousands, unless otherwise specified	Jul. 31, 2014		Jul. 31, 2013
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, Fair Value Disclosure	$ 98,928		$ 121,541
Cash and Cash Equivalents
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, Fair Value Disclosure	59,269	[1]	28,235	[1]
Marketable Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, Fair Value Disclosure	39,659		93,306	[2]
Fair Value, Inputs, Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, Fair Value Disclosure	63,243		36,788
Fair Value, Inputs, Level 1 | Cash and Cash Equivalents
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, Fair Value Disclosure	59,269	[1]	28,235	[1]
Fair Value, Inputs, Level 1 | Marketable Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, Fair Value Disclosure	3,974		8,553	[2]
Fair Value, Inputs, Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, Fair Value Disclosure	35,685		84,753
Fair Value, Inputs, Level 2 | Marketable Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, Fair Value Disclosure	$ 35,685		$ 84,753	[2]

[1] Cash and cash equivalents as of July 31, 2014 and July 31, 2013 includes cash held in operating accounts of approximately $56.0 million and $25.9 million, respectively, that are not subject to fair value measurements. For purposes of this disclosure they are included as having Level 1 inputs.

[2] Marketable securities at July 31, 2013 excluded approximately $2.8 million of commercial paper which is held-to-maturity and not subject to fair value measurements.