Financial Assets and Liabilities Measured at Fair Value and Related Valuation Inputs (Detail) (USD $) In Thousands, unless otherwise specified	Oct. 31, 2013		Jul. 31, 2013
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, Fair Value Disclosure	$ 117,985		$ 121,541
Cash and Cash Equivalents
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, Fair Value Disclosure	30,716	[1]	28,235	[1]
Marketable securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, Fair Value Disclosure	87,269	[2]	93,306	[2]
Fair Value, Inputs, Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, Fair Value Disclosure	42,540		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	30,716	[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	11,824	[2]	8,553	[2]
Fair Value, Inputs, Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, Fair Value Disclosure	75,445		84,753
Fair Value, Inputs, Level 2 | Marketable securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, Fair Value Disclosure	$ 75,445	[2]	$ 84,753	[2]

[1] Cash and cash equivalents as of October 31, 2013 and July 31, 2013 included cash held in operating accounts of approximately $25.3 million and $25.9 million, respectively that were not subject to fair value measurements. For purposes of this disclosure they are included as having Level 1 inputs.

[2] Marketable securities as of October 31, 2013 and July 31, 2013 excluded approximately $0 million and $2.8 million, respectively, of commercial paper which was held-to-maturity and not subject to fair value measurements.