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Income taxes Income taxes (Details) - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended
Jul. 31, 2015
Jul. 31, 2015
Jul. 31, 2014
Income Tax Contingency [Line Items]      
effective income tax rate from continuing operations   4.90% 21.40%
Unrecognized tax benefits $ 100 $ 100  
Unrecognized tax benefits that would impact effective tax rate 100 100  
Unrecognized tax benefits, income tax penalties and interest expense 2    
Unrecognized tax benefits, income tax penalties and interest accrued $ 36 $ 36  
Open tax year beginning   2012  
Open tax years up to the amount of research tax credit generated   January 31, 2002 through January 31, 2012  
Operating loss carryforwards, expiration dates beginning   Jan. 31, 2030