Business and segment information Segment reporting (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Jan. 31, 2014 Segments	Jan. 31, 2013
Segment information [Line Items]
Entity Incorporation, Date of Incorporation	Oct. 12, 1993
Number of reportable segments	2
Customer concentration risk, percentage	24.50%
Net sales	$ 226,835	$ 168,807
Gross profit	52,215	27,494
Income (loss) from operations	13,083	(8,820)
Total assets	163,269	149,488
Capital expenditures	2,761	5,360
Depreciation and amortization expense	5,785	5,806
Interest expense, net	1,311	1,498
Piping Systems [Member]
Segment information [Line Items]
Net sales	158,422	89,664
Gross profit	43,273	17,020
Income (loss) from operations	24,213	3,452
Total assets	109,154	83,944
Capital expenditures	2,425	4,206
Depreciation and amortization expense	3,489	3,344
Interest expense, net	(495)	(226)
Filtration Products [Member]
Segment information [Line Items]
Net sales	68,413	79,143
Gross profit	8,942	10,474
Income (loss) from operations	(1,629)	(2,962)
Total assets	41,765	52,958
Capital expenditures	294	995
Depreciation and amortization expense	1,729	1,750
Interest expense, net	(1,966)	(2,239)
Asset Impairment Charges	0	1,520
Corporate and Other [Member]
Segment information [Line Items]
Income (loss) from operations	(9,501)	(9,310)
Total assets	12,350	12,586
Capital expenditures	42	159
Depreciation and amortization expense	567	712
Interest expense, net	$ 1,150	$ 967
Sales Revenue, Net [Member]
Segment information [Line Items]
Customer concentration risk, percentage	10.60%	10.00%