Summary of Significant Accounting Policies - Additional Information (Detail) (USD $)	12 Months Ended
	Jul. 31, 2014	Jul. 31, 2013	Jul. 31, 2012	Jul. 31, 2011	Aug. 31, 2008	Aug. 29, 2008
Significant Accounting Policies [Line Items]
Inventory reserves	$ 45,300,000	$ 41,800,000
Estimated weighted average useful life of acquired intangible assets	4 years 3 months 18 days
Indefinite lived trademarks	6,700,000
Warranty for Products	The Company generally offers a warranty for most of its products, the standard terms and conditions of which are based on the product sold and the customer.
Cost of sales	4,700,000	2,700,000	3,400,000
Provision for (benefit from) income taxes	767,000	(275,000)	(938,000)
Unrecognized income tax benefits	6,590,000	6,788,000	8,009,000	9,094,000
Unrecognized income tax benefits that would impact income tax rate if recognized	3,000,000	3,200,000
Uncertain tax positions accrued interest and penalties	1,000,000	900,000
Ownership percentage that trigger limitation on NOL carryforward utilization					50.00%	50.00%
Operating loss carryforwards, limitations on use	As a result of the merger with Credence on August 29, 2008, a greater than 50% cumulative ownership change in both entities triggered a significant limitation on net operating loss carryforward utilization. The Company's ability to use the acquired U.S. net operating loss and credit carryforwards is subject to annual limitation as defined in sections 382 and 383 of the Internal Revenue Code
Estimated annual limitation on use of net operating loss					10,100,000	10,100,000
Amount of net operating loss currently available for utilization	202,000,000					202,000,000
Unrecognized stock-based compensation expense expected to be recognized	11,200,000
Stock-based compensation expense recognition period	3 years 9 months 18 days
Maturity period of highly liquid investments to be considered cash equivalent	3 months
Allowance for doubtful accounts receivable, write-offs	0.1	0.0	0.0
Depreciation Expense	6,800,000	6,500,000	7,800,000
Stock Option
Significant Accounting Policies [Line Items]
Anti-dilutive securities excluded from computation of earnings per share	400,000	1,000,000	1,200,000
ECT and Multitest
Significant Accounting Policies [Line Items]
Estimated weighted average useful life of acquired intangible assets	8 years
Provision for (benefit from) income taxes	(500,000)
Restricted stock units (RSU's)
Significant Accounting Policies [Line Items]
Restricted stock unit awards granted during period	1,109,100	895,900	939,600
Anti-dilutive securities excluded from computation of earnings per share		2,000,000	1,800,000
Restricted stock units (RSU's) | Executives
Significant Accounting Policies [Line Items]
Restricted stock unit awards granted during period	445,000	390,000	465,000
Foreign
Significant Accounting Policies [Line Items]
Provision for (benefit from) income taxes	$ 1,300,000
Maximum
Significant Accounting Policies [Line Items]
Property plant and equipment estimated useful life	7 years	7 years
Maximum | Restricted stock units (RSU's)
Significant Accounting Policies [Line Items]
Restricted stock unit award granted vesting period	4 years
Minimum
Significant Accounting Policies [Line Items]
Property plant and equipment estimated useful life	3 years	3 years
Minimum | Restricted stock units (RSU's)
Significant Accounting Policies [Line Items]
Restricted stock unit award granted vesting period	1 year