Derivative Instruments (Details) (USD $)	3 Months Ended
	Apr. 30, 2012	Apr. 30, 2011
Derivative Instruments [Abstract]
Net foreign currency exchange loss	$ 3,500,000	$ 6,900,000
Average notional amounts of derivative financial instruments outstanding	$ 1,700,000,000	$ 1,500,000,000
Average maturities of derivatives, days	28 days	37 days