Financial instruments (Details 1) (USD $) In Thousands	Jul. 31, 2011
Receivables [Member]
Fair value of foreign currency forward contracts
Derivative Asset Not Designated as Hedging Instrument, Fair Value	$ 3,986
Accrued Liabilities [Member]
Fair value of foreign currency forward contracts
Derivative Liability Not Designated as Hedging Instrument, Fair Value	$ 416

Fair value as of the balance sheet date of all foreign currency derivative liabilities not designated as hedging instruments.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 133
-Paragraph 17

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