Selected Balance Sheet Information (Details) (USD $) In Thousands, unless otherwise specified	Apr. 30, 2013	Jan. 31, 2013	Apr. 30, 2012	Jan. 31, 2012
Accounts receivable, net:
Trade accounts	$ 59,443	$ 56,508	$ 58,811
Allowance for doubtful accounts	(205)	(205)	(170)
Accounts receivable, net	59,238	56,303	58,641
Inventories:
Finished goods	8,533	8,571	7,688
In process	2,673	2,675	6,847
Materials	37,825	34,943	40,129
Inventories	49,031	46,189	54,664
Property, plant and equipment, net:
Property, plant and equipment	164,180	156,658	134,407
Accumulated depreciation	(78,081)	(75,420)	(69,519)
Property, plant and equipment, net	86,099	81,238	64,888
Accrued liabilities:
Salaries and benefits	2,726	3,978	2,635
Vacation	4,384	4,025	4,584
401(k) contributions	319	520	555
Insurance obligations	2,458	2,506	2,887
Profit sharing	88	287	413
Warranties	1,990	1,888	1,792	1,699
Acquisition-related contingent liabilities	845	712	6,658
Taxes - accrued and withheld	7,774	1,392	11,300
Other	1,148	1,884	1,141
Accrued liabilities	21,732	17,192	31,965
Other liabilities:
Postretirement benefits	8,120	8,072	7,423
Acquisition-related contingent consideration	2,076	2,359	2,169
Deferred income taxes	2,475	2,453	3,944
Uncertain tax positions	6,116	5,818	5,395
Other liabilities	$ 18,787	$ 18,702	$ 18,931