Selected Balance Sheet Information (Details) (USD $) In Thousands, unless otherwise specified	Oct. 31, 2012	Jul. 31, 2012	Jan. 31, 2012	Oct. 31, 2011	Jul. 31, 2011	Jan. 31, 2011
Accounts Receivable, net:
Trade accounts	$ 55,667		$ 60,929	$ 50,861
Allowance for doubtful accounts	(205)		(170)	(200)
Accounts Receivable, Net, Current	55,462		60,759	50,661
Inventories:
Finished goods	8,347		7,094	7,713
In process	3,647		6,105	8,238
Materials	38,030		41,557	33,905
Inventories	50,024		54,756	49,856
Property, plant and equipment, net:
Property, Plant and equipment	151,122		128,948	121,988
Accumulated depreciation	(73,730)		(67,054)	(65,082)
Property, plant and equipment, net	77,392		61,894	56,906
Accrued liabilities:
Salaries and benefits	4,425		4,297	3,983
Vacation	4,038		4,387	3,695
401(k) contributions	500		966	287
Insurance obligations	2,949		2,789	2,314
Profit sharing	750		1,244	880
Warranties	1,879	1,949	1,699	1,339	1,642	1,437
Acquisition-related contingent consideration	7,154		3,266	175
Taxes - Accrued and withheld	1,990		2,596	2,912
Other	1,563		1,749	1,189
Accrued liabilities	25,248		22,993	16,774
Other liabilities:
Postretirement benefits	7,589		7,348	5,949
Acquisition-related contingent consideration	2,231		7,655	2,095
Deferred income taxes	3,477		4,518	550
Uncertain tax positions	5,881		4,946	4,988
Other liabilities	$ 19,178		$ 24,467	$ 13,582