Selected Balance Sheet Information (Details) (USD $) In Thousands, unless otherwise specified	Jul. 31, 2012	Apr. 30, 2012	Jan. 31, 2012	Jul. 31, 2011	Apr. 30, 2011	Jan. 31, 2011
Accounts Receivable, net:
Trade accounts	$ 50,055		$ 60,929	$ 43,510
Allowance for doubtful accounts	(170)		(170)	(262)
Accounts Receivable, Net, Current	49,885		60,759	43,248
Inventories:
Finished goods	7,394		7,094	7,780
In process	4,979		6,105	7,687
Materials	38,016		41,557	34,782
Inventories	50,389		54,756	50,249
Property, plant and equipment, net:
Property, Plant and equipment	145,433		128,948	111,518
Accumulated depreciation	(72,244)		(67,054)	(63,507)
Property, plant and equipment, net	73,189		61,894	48,011
Accrued liabilities:
Salaries and benefits	2,993		4,297	2,356
Vacation	4,155		4,387	3,484
401(k) contributions	611		966	271
Insurance obligations	3,003		2,789	3,085
Profit sharing	612		1,244	536
Warranties	1,949	1,792	1,699	1,642	1,631	1,437
Acquisition-related contingent consideration	7,028		3,266	271
Taxes - Accrued and withheld	1,999		2,596	2,244
Other	1,621		1,749	998
Accrued liabilities	23,971		22,993	14,887
Other liabilities:
Postretirement benefits	7,520		7,348	5,880
Acquisition-related contingent consideration	2,108		7,655	2,076
Deferred income taxes	3,919		4,518	517
Uncertain tax positions	5,657		4,946	4,756
Other liabilities	$ 19,204		$ 24,467	$ 13,229