Selected Balance Sheet Information (Details) (USD $) In Thousands, unless otherwise specified	Oct. 31, 2014	Jul. 31, 2014	Jan. 31, 2014	Oct. 31, 2013	Jul. 31, 2013	Jan. 31, 2013
Accounts receivable, net:
Trade accounts	$ 54,889		$ 54,962	$ 64,164
Allowance for doubtful accounts	(356)		(319)	(204)
Accounts receivable, net	54,533		54,643	63,960
Inventories:
Finished goods	7,981		7,232	7,591
In process	2,063		2,131	2,743
Materials	41,756		45,502	41,062
Inventories	51,800		54,865	51,396
Property, plant and equipment, net:
Property, plant and equipment	195,487		182,700	177,428
Accumulated depreciation	(95,118)		(84,624)	(81,624)
Property, plant and equipment, net	100,369		98,076	95,804
Accrued liabilities:
Salaries and benefits	2,061		1,858	3,120
Vacation	3,613		3,700	4,149
401(k) contributions	473		727	446
Insurance obligations	2,171		2,428	2,496
Warranties	2,456	2,617	2,525	2,210	2,047	1,888
Acquisition-related contingent liabilities	1,191		890	730
Taxes - accrued and withheld	2,624		1,743	3,754
Other	2,333		2,377	1,689
Accrued liabilities	16,922		16,248	18,594
Other liabilities:
Postretirement benefits	8,264		7,998	8,304
Acquisition-related contingent consideration,	3,587		2,457	2,323
Deferred income taxes	1,406		3,526	1,824
Uncertain tax positions	7,175		6,557	6,206
Other liabilities	$ 20,432		$ 20,538	$ 18,657