Financial Assets and Liabilities Measured at Fair Value and Related Valuation Inputs (Detail) (USD $) In Thousands, unless otherwise specified	Jan. 31, 2013		Jul. 31, 2012
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, Fair Value Disclosure	$ 121,886		$ 134,378
Cash and Cash Equivalents
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, Fair Value Disclosure	32,358	[1]	29,446	[1]
Marketable securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, Fair Value Disclosure	89,528	[2]	104,932	[2]
Fair Value, Inputs, Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, Fair Value Disclosure	41,693		36,307
Fair Value, Inputs, Level 1 | Cash and Cash Equivalents
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, Fair Value Disclosure	32,358	[1]	29,081	[1]
Fair Value, Inputs, Level 1 | Marketable securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, Fair Value Disclosure	9,335	[2]	7,226	[2]
Fair Value, Inputs, Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, Fair Value Disclosure	80,193		98,071
Fair Value, Inputs, Level 2 | Cash and Cash Equivalents
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, Fair Value Disclosure		[1]	365	[1]
Fair Value, Inputs, Level 2 | Marketable securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, Fair Value Disclosure	80,193	[2]	97,706	[2]
Fair Value, Inputs, Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, Fair Value Disclosure
Fair Value, Inputs, Level 3 | Cash and Cash Equivalents
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, Fair Value Disclosure		[1]		[1]
Fair Value, Inputs, Level 3 | Marketable securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, Fair Value Disclosure		[2]		[2]

[1] Cash and cash equivalents as of January 31, 2013 and July 31, 2012 includes cash held in operating accounts of approximately $0.0 million and $28.6 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 as of January 31, 2013 and July 31, 2012 excludes approximately $0.0 million and $2.8 million, respectively, of commercial paper which is held to maturity and not subject to fair value measurements.