Significant accounting policies Concentration of credit risk (Details)	12 Months Ended
	Jan. 31, 2017	Jan. 31, 2016
Concentration Risk [Line Items]
portion of customers accounts receivable paid	35.40%
Sales Revenue, Net [Member]
Concentration Risk [Line Items]
Customer concentration risk, percentage		10.30%
Accounts Receivable [Member]
Concentration Risk [Line Items]
Customer concentration risk, percentage	33.20%	46.50%