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Stock-based compensation Stock-based compensation expense (Details) (USD $)
3 Months Ended 6 Months Ended
Jul. 31, 2012
Jul. 31, 2011
Jul. 31, 2012
Jul. 31, 2011
Stock-based compensation expense [Abstract]        
Stock-based compensation expense $ 174,000 $ 69,000 $ 260,000 $ 297,000
unrecognized compensation expense related to unvested stock options $ 1,200,000   $ 1,200,000  
expense is expected to be recognized over a period     2 years 10 months 24 days