Employee Stock and Savings Plans - Stock Compensation Expense Recognized (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Apr. 30, 2013	Apr. 30, 2012
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation	$ 6,566	$ 5,147
Cost of goods sold
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation	460	319
Research and development
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation	2,610	2,117
Marketing and selling
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation	1,882	1,549
General and administration
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation	$ 1,614	$ 1,162
Omnibus Incentive Plan [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Award requisite service period	4 years
Award expiry period from date of grant	10 years
Employee stock purchase plans
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Maximum number of shares that may be purchased by eligible participants (in shares)	6,000
Eligible employee stock purchase price	85.00%
Employee stock purchase plan offering term	6 months