Interest expense, net (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Oct. 31, 2012	Oct. 31, 2011	Oct. 31, 2012	Oct. 31, 2011
Interest expense, net [Abstract]
Interest expense	$ 673	$ 584	$ 1,757	$ 1,655
Interest income	(79)	(189)	(372)	(641)
Interest expense, net	$ 594	$ 395	$ 1,385	$ 1,014