Significant accounting policies Concentration of credit risk (Details)	12 Months Ended
	Jan. 31, 2016	Jan. 31, 2015
Concentration Risk [Line Items]
portion of customers accounts receivable paid	40.40%
Sales Revenue, Net [Member]
Concentration Risk [Line Items]
Customer concentration risk, percentage	10.30%	17.20%
Accounts Receivable [Member]
Concentration Risk [Line Items]
Customer concentration risk, percentage	46.40%	37.40%