Financial instruments (Details) (USD $) In Thousands, unless otherwise specified	Jan. 31, 2012
Summarized values by currency and forward exchange contracts outstanding
Notional amount of foreign currency derivative sale contracts	$ 43,764
Fair market value of Foreign currency derivative sale contracts	43,752
Notional amount of foreign currency derivative purchase contracts	176,091
Fair market value of Foreign currency derivative purchase contracts	175,479
Euro [Member]
Summarized values by currency and forward exchange contracts outstanding
Notional amount of foreign currency derivative sale contracts	6,368
Fair market value of Foreign currency derivative sale contracts	6,229
Notional amount of foreign currency derivative purchase contracts	88,754
Fair market value of Foreign currency derivative purchase contracts	86,573
British Pound [Member]
Summarized values by currency and forward exchange contracts outstanding
Notional amount of foreign currency derivative sale contracts	20,577
Fair market value of Foreign currency derivative sale contracts	20,585
Notional amount of foreign currency derivative purchase contracts	46,020
Fair market value of Foreign currency derivative purchase contracts	46,305
Japanese Yen [Member]
Summarized values by currency and forward exchange contracts outstanding
Notional amount of foreign currency derivative sale contracts	4,432
Fair market value of Foreign currency derivative sale contracts	4,433
Notional amount of foreign currency derivative purchase contracts	7,185
Fair market value of Foreign currency derivative purchase contracts	7,259
Others [Member]
Summarized values by currency and forward exchange contracts outstanding
Notional amount of foreign currency derivative sale contracts	12,387
Fair market value of Foreign currency derivative sale contracts	12,505
Notional amount of foreign currency derivative purchase contracts	34,132
Fair market value of Foreign currency derivative purchase contracts	$ 35,342