Derivative Instruments (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 31, 2015	Jul. 31, 2014	Jul. 31, 2015	Jul. 31, 2014
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Net foreign currency exchange (gain) loss	$ (5,900)	$ (3,300)	$ 2,100	$ 5,500
Notional amount of derivative financial instruments outstanding	$ 600,000	$ 600,000	$ 500,000	$ 700,000
Average maturities of derivatives, days	33 days	35 days	35 days	35 days