Selected Balance Sheet Information (Details) (USD $) In Thousands, unless otherwise specified	Jan. 31, 2012	Jan. 31, 2011	Jan. 31, 2010	Jan. 31, 2009
Accounts receivable, net:
Accounts receivable, net	$ 60,759	$ 39,967	$ 34,327
Inventories:
Finished goods	7,094	7,994	6,283
In process	6,105	5,424	4,172
Materials	41,557	30,261	24,020
Inventories	54,756	43,679	34,475
Other current assets:
Insurance policy benefit	1,873	1,909	2,300
Prepaid expenses and other	1,030	1,330	490
Other current assets	2,903	3,239	2,790
Property, plant and equipment, net:
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	67,054	60,558	55,290
Property, plant and equipment, net	61,894	41,522	33,029
Other assets, net:
Investment in affiliate	4,409	4,728	5,010
Deferred income taxes	0	924	1,580
Other, net	155	43	59
Other assets, net	4,564	5,695	6,649
Accrued liabilities:
Salaries and benefits	4,297	3,264	1,148
Vacation	4,387	3,186	2,693
401 (k) contributions	966	253	180
Insurance obligations	2,789	3,356	3,959
Profit sharing	1,244	1,627	217
Warranties	1,699	1,437	1,259	1,004
Taxes - accrued and withheld	2,596	1,453	1,574
Acquisition-related contingent consideration	3,266	263	103
Other	1,749	1,257	1,123
Accrued liabilities	22,993	16,096	12,256
Other liabilities:
Postretirement benefits	7,348	5,757	5,283
Acquisition-related contingent consideration	7,655	2,230	2,301
Deferred income taxes	4,518	0	0
Uncertain tax positions	4,946	4,224	3,514
Other liabilities	24,467	12,211	11,098
Trade accounts [Member]
Accounts receivable, net:
Accounts Receivable, Gross, Current	60,929	40,267	34,624
Allowance for Doubtful Accounts Receivable, Current	(170)	(300)	(297)
Accounts receivable, net	60,759	39,967	34,327
Land [Member]
Property, plant and equipment, net:
Property, Plant and Equipment, Gross	2,077	1,798	1,227
Building and improvements [Member]
Property, plant and equipment, net:
Property, Plant and Equipment, Gross	36,952	24,972	22,973
Machinery and Equipment [Member]
Property, plant and equipment, net:
Property, Plant and Equipment, Gross	$ 89,919	$ 75,310	$ 64,119