Financial instruments (Details) (USD $) In Thousands	Jul. 31, 2011
Outstanding foreign currency forward contracts
Notional amount of foreign currency derivative sale contracts	$ 31,370
Fair market value of foreign currency derivative sale contracts	31,975
Notional amount of foreign currency derivative purchase contracts	173,867
Fair market value of foreign currency derivative purchase contracts	178,042
Euro [Member]
Outstanding foreign currency forward contracts
Notional amount of foreign currency derivative sale contracts	14,623
Fair market value of foreign currency derivative sale contracts	14,680
Notional amount of foreign currency derivative purchase contracts	92,340
Fair market value of foreign currency derivative purchase contracts	93,840
British pound [Member]
Outstanding foreign currency forward contracts
Notional amount of foreign currency derivative sale contracts	1,632
Fair market value of foreign currency derivative sale contracts	1,647
Notional amount of foreign currency derivative purchase contracts	38,807
Fair market value of foreign currency derivative purchase contracts	39,188
Japanese yen [Member]
Outstanding foreign currency forward contracts
Notional amount of foreign currency derivative sale contracts	10,096
Fair market value of foreign currency derivative sale contracts	10,460
Notional amount of foreign currency derivative purchase contracts	11,455
Fair market value of foreign currency derivative purchase contracts	11,757
Others [Member]
Outstanding foreign currency forward contracts
Notional amount of foreign currency derivative sale contracts	5,019
Fair market value of foreign currency derivative sale contracts	5,188
Notional amount of foreign currency derivative purchase contracts	31,265
Fair market value of foreign currency derivative purchase contracts	$ 33,257

Fair value as of the balance sheet date of foreign currency derivative assets, which includes all such derivative instruments in hedging and nonhedging relationships that are recognized as assets on the balance sheet.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 107
-Paragraph 10

+ Details

Name:	us-gaap_ForeignCurrencyDerivativeAssetsAtFairValue
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value as of the balance sheet date of interest rate derivative liabilities, which includes all such derivative instruments in hedging and nonhedging relationships that are recognized as liabilities on the balance sheet.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 107
-Paragraph 10

+ Details

Name:	us-gaap_ForeignCurrencyDerivativeLiabilitiesAtFairValue
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_ForeignCurrencyDerivativesAbstract
Namespace Prefix:	us-gaap
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Aggregate notional amount of foreign currency derivatives to purchase a foreign currency. Notional amount refers to the number of currency units specified in the foreign currency derivative contract.

+ Details

Name:	us-gaap_NotionalAmountOfForeignCurrencyDerivativePurchaseContracts
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Aggregate notional amount of foreign currency derivatives to sell a foreign currency. Notional amount refers to the number of currency units specified in the foreign currency derivative contract.

+ Details

Name:	us-gaap_NotionalAmountOfForeignCurrencyDerivativeSaleContracts
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant