Derivative Instruments (Narrative) (Details) (USD $)	12 Months Ended
	Jan. 31, 2013	Jan. 31, 2012	Jan. 31, 2011
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Net foreign currency exchange loss	$ 13,100,000	$ 8,700,000	$ 4,700,000
Notional amount of derivative financial instruments outstanding	$ 1,800,000,000	$ 1,500,000,000
Average maturities of derivatives, days	27 days	37 days