Business information Geographic information (Details) - USD ($) $ in Thousands	12 Months Ended
	Jan. 31, 2018	Jan. 31, 2017
Geographic information [Line Items]
foreign sales	59.50%	57.00%
Net sales	$ 105,248	$ 98,845
Property, plant and equipment, net of accumulated depreciation	34,509	36,275
United States
Geographic information [Line Items]
Net sales	42,648	42,048
Property, plant and equipment, net of accumulated depreciation	11,307	11,747
Canada
Geographic information [Line Items]
Net sales	31,206	25,915
Property, plant and equipment, net of accumulated depreciation	13,868	13,276
Middle East [Member]
Geographic information [Line Items]
Net sales	26,322	28,009
Property, plant and equipment, net of accumulated depreciation	9,119	10,987
India
Geographic information [Line Items]
Net sales	1,317	2,360
Property, plant and equipment, net of accumulated depreciation	215	265
Other
Geographic information [Line Items]
Net sales	$ 3,755	$ 513