Selected Balance Sheet Information (Details) (USD $) In Thousands, unless otherwise specified	Apr. 30, 2014	Jan. 31, 2014	Apr. 30, 2013	Jan. 31, 2013
Accounts receivable, net:
Trade accounts	$ 55,574	$ 54,962	$ 59,443
Allowance for doubtful accounts	(319)	(319)	(205)
Accounts receivable, net	55,255	54,643	59,238
Inventories:
Finished goods	6,995	7,232	8,533
In process	1,822	2,131	2,673
Materials	46,249	45,502	37,825
Inventories	55,066	54,865	49,031
Property, plant and equipment, net:
Property, plant and equipment	184,861	182,700	164,180
Accumulated depreciation	(88,116)	(84,624)	(78,081)
Property, plant and equipment, net	96,745	98,076	86,099
Accrued liabilities:
Salaries and benefits	2,446	1,858	2,814
Vacation	3,981	3,700	4,384
401(k) contributions	353	727	319
Insurance obligations	2,359	2,428	2,458
Warranties	2,654	2,525	1,990	1,888
Acquisition-related contingent liabilities	628	890	845
Taxes - accrued and withheld	6,735	1,743	7,774
Other	1,495	2,377	1,148
Accrued liabilities	20,651	16,248	21,732
Other liabilities:
Postretirement benefits	8,068	7,998	8,120
Acquisition-related contingent consideration	2,056	2,457	2,076
Deferred income taxes	2,531	3,526	2,475
Uncertain tax positions	6,744	6,557	6,116
Other liabilities	$ 19,399	$ 20,538	$ 18,787