Financial instruments - Outstanding Foreign Currency Forward Contracts (Detail) (USD $) In Thousands, unless otherwise specified	Jan. 31, 2013
Derivative [Line Items]
Notional Amounts of foreign currency derivative sale contracts	$ 10,524
Fair Market Value of foreign currency derivative sale contracts	10,704
Notional Amounts of foreign currency derivative purchase contracts	170,192
Fair Market Value of foreign currency derivative purchase contracts	174,554
Euro [Member]
Derivative [Line Items]
Notional Amounts of foreign currency derivative sale contracts	4,674
Fair Market Value of foreign currency derivative sale contracts	4,865
Notional Amounts of foreign currency derivative purchase contracts	97,771
Fair Market Value of foreign currency derivative purchase contracts	102,137
British pound [Member]
Derivative [Line Items]
Notional Amounts of foreign currency derivative sale contracts
Fair Market Value of foreign currency derivative sale contracts
Notional Amounts of foreign currency derivative purchase contracts	28,427
Fair Market Value of foreign currency derivative purchase contracts	28,414
Japanese yen [Member]
Derivative [Line Items]
Notional Amounts of foreign currency derivative sale contracts	1,650
Fair Market Value of foreign currency derivative sale contracts	1,603
Notional Amounts of foreign currency derivative purchase contracts	4,756
Fair Market Value of foreign currency derivative purchase contracts	4,275
Australian dollar [Member]
Derivative [Line Items]
Notional Amounts of foreign currency derivative sale contracts	522
Fair Market Value of foreign currency derivative sale contracts	521
Notional Amounts of foreign currency derivative purchase contracts	9,131
Fair Market Value of foreign currency derivative purchase contracts	9,124
Singapore dollar [Member]
Derivative [Line Items]
Notional Amounts of foreign currency derivative sale contracts
Fair Market Value of foreign currency derivative sale contracts
Notional Amounts of foreign currency derivative purchase contracts	8,911
Fair Market Value of foreign currency derivative purchase contracts	8,835
Others [Member]
Derivative [Line Items]
Notional Amounts of foreign currency derivative sale contracts	3,678
Fair Market Value of foreign currency derivative sale contracts	3,715
Notional Amounts of foreign currency derivative purchase contracts	21,196
Fair Market Value of foreign currency derivative purchase contracts	$ 21,769