Tax Effects of Temporary Differences and Carryforwards on Deferred Tax Assets and Liabilities (Detail) (USD $) In Thousands, unless otherwise specified	Jan. 31, 2012	Jan. 31, 2011
Deferred tax assets:
Depreciation of property, plant, and equipment	$ 232	$ 1,393
Reserves and allowances	9,509	3,746
Accrued expenses not currently deductible	22,267	25,337
Stock-based compensation expense	14,902	14,832
Net operating loss carryforwards	68,746	56,221
Tax credit carryforwards	57,198	47,163
Purchased technology and other intangible assets	15,070	16,365
Deferred revenue	1,563	1,793
Other, net	8,086	8,427
Total gross deferred tax assets	197,573	175,277
Less valuation allowance	(147,984)	(133,036)
Deferred tax assets	49,589	42,241
Deferred tax liabilities:
Intangible assets	(21,578)	(22,572)
Convertible debt	(15,607)	(2,808)
Deferred tax liabilities	(37,185)	(25,380)
Net deferred tax assets	$ 12,404	$ 16,861