Business and segment information Segment reporting (Details) $ in Thousands	12 Months Ended
	Jan. 31, 2016 USD ($) Segments	Jan. 31, 2015 USD ($)
Segment information [Line Items]
Entity Incorporation, Date of Incorporation	Oct. 12, 1993
Number of reportable segments | Segments	1
Net sales	$ 122,696	$ 126,923
Gross profit	26,741	30,774
Income (loss) from operations
Income (loss) from operations	2,878	5,847
Segment assets	138,123	148,074
Capital expenditures	5,051	4,438
Depreciation and amortization	4,204	4,187
Piping Systems [Member]
Segment information [Line Items]
Net sales	122,696	126,923
Gross profit	26,741	30,774
Income (loss) from operations
Income (loss) from operations	10,537	12,740
Segment assets	112,161	99,065
Capital expenditures	4,762	3,953
Depreciation and amortization	3,735	3,635
Corporate [Member]
Income (loss) from operations
Income (loss) from operations	(7,659)	(6,893)
Segment assets	10,229	7,533
Capital expenditures	289	485
Depreciation and amortization	469	552
Operating Segments [Member]
Income (loss) from operations
Segment assets	$ 122,390	$ 106,598