Significant accounting policies Long lived assets (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Jan. 31, 2014	Jan. 31, 2013
Long lived assets [Abstract]
Depreciation and amortization expense	$ 5,785	$ 5,806
Land, buildings and improvements	36,535	36,572
Machinery and equipment	50,793	49,919
Furniture, office equipment and computer systems	9,723	11,065
Transportation equipment	206	189
Subtotal	97,257	97,745
Less accumulated depreciation and amortization	54,716	52,163
Property, plant and equipment, net of accumulated depreciation	42,541	45,582
Filtration Products [Member]
Long lived assets [Abstract]
Asset Impairment Charges	0	1,520
Depreciation and amortization expense	$ 1,729	$ 1,750