Interest expense, net (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jul. 31, 2013	Jul. 31, 2012	Jul. 31, 2013	Jul. 31, 2012
Interest expense, net [Abstract]
Interest expense	$ 518	$ 518	$ 1,062	$ 953
Interest income	(115)	(165)	(222)	(295)
Interest expense, net	$ 403	$ 353	$ 840	$ 658