Significant accounting policies Restricted cash (Details) - USD ($) $ in Thousands	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2016
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents	$ 7,084	$ 7,603
Restricted cash	1,237	1,098
Cash, cash equivalents and restricted cash	8,321	8,701	$ 18,955
United States
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents	700	200
Foreign
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents	$ 6,400	$ 7,400