Selected Balance Sheet Information (Details) (USD $) In Thousands, unless otherwise specified	Oct. 31, 2013	Jul. 31, 2013	Jan. 31, 2013	Oct. 31, 2012	Jul. 31, 2012	Jan. 31, 2012
Accounts receivable, net:
Trade accounts	$ 64,164		$ 56,508	$ 55,667
Allowance for doubtful accounts	(204)		(205)	(205)
Accounts receivable, net	63,960		56,303	55,462
Inventories:
Finished goods	7,591		8,571	8,347
In process	2,743		2,675	3,647
Materials	41,062		34,943	38,030
Inventories	51,396		46,189	50,024
Property, plant and equipment, net:
Property, plant and equipment	177,428		156,658	151,122
Accumulated depreciation	(81,624)		(75,420)	(73,730)
Property, plant and equipment, net	95,804		81,238	77,392
Accrued liabilities:
Salaries and benefits	3,120		4,265	5,175
Vacation	4,149		4,025	4,038
401(k) contributions	446		520	500
Insurance obligations	2,496		2,506	2,949
Warranties	2,210	2,047	1,888	1,879	1,949	1,699
Taxes - accrued and withheld	3,754		1,392	1,990
Other	1,689		1,884	1,563
Accrued liabilities	18,594		17,192	25,248
Other liabilities:
Postretirement benefits	8,304		8,072	7,589
Acquisition-related contingent consideration	2,323		2,359	2,231
Deferred income taxes	1,824		2,453	3,477
Uncertain tax positions	6,206		5,818	5,881
Other liabilities	18,657		18,702	19,178
Acquisition-related contingent liabilities	$ 730		$ 712	$ 7,154