Computation of Basic and Diluted Net Loss Per Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Oct. 31, 2011	Oct. 31, 2010	Oct. 31, 2011	Oct. 31, 2010
Earnings Per Share Disclosure [Line Items]
Net income (loss)	$ 24,071	$ 15,257	$ 26,052	$ (22,015)
Weighted average common shares used to calculate basic net income (loss) per share	109,501	109,364	110,423	106,942
Employee stock options, restricted stock units and employee stock purchase plan	2,062	2,775	2,758
Weighted average common and potential common shares used to calculate diluted net income (loss) per share	111,563	112,139	113,181	106,942
Basic net income (loss) per share	$ 0.22	$ 0.14	$ 0.24	$ (0.21)
Diluted net income (loss) per share	$ 0.22	$ 0.14	$ 0.23	$ (0.21)