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Hedging Instruments (Details Textual) (USD $)
6 Months Ended 3 Months Ended
Jul. 31, 2012
Jul. 31, 2012
Interest rate swaps [Member]
Jul. 31, 2012
Platinum [Member]
Ounces
Jul. 31, 2012
Silver [Member]
Ounces
Hedging Instruments (Textual) [Abstract]        
Notional amount of precious metal hedge     14,800 403,000
Payment for settlement of interest rate swaps $ (29,335,000) $ (29,335,000)    
Hedging Instruments (Additional Textual) [Abstract]        
Notional amount of foreign exchange forward and put option contracts as cash flow hedges 139,500,000      
Notional amount of foreign exchange forward contracts as undesignated hedges 67,648,000      
Expected approximate amount of net pre-tax derivative losses included in accumulated other comprehensive income that will be reclassified into earnings within the next 12 months $ 9,270,000