Selected Balance Sheet Information (Details) - USD ($) $ in Thousands	Oct. 31, 2015	Apr. 30, 2015	Jan. 31, 2015	Oct. 31, 2014	Apr. 30, 2014	Jan. 31, 2014
Accounts receivable, net:
Trade accounts	$ 40,062		$ 56,895	$ 54,889
Allowance for doubtful accounts	(769)		(319)	(356)
Accounts receivable, net	39,293		56,576	54,533
Inventories:
Finished goods	5,211		8,127	7,981
In process	2,157		1,317	2,063
Materials	41,256		45,708	41,756
Inventories	48,624		55,152	51,800
Other current assets:
Insurance policy benefit	728		733	517
Federal tax receivable	0		713	0
Receivable from sale of business	420		0	0
Prepaid Expense and other	1,767		1,648	2,364
Other current assets	2,915		3,094	2,881
Property, plant and equipment, net:
Property, plant and equipment, net	117,760		117,513	100,369
Other Assets, net (Noncurrent):
Investment in affiliate (equity method)	2,720		3,217	3,175
Other, net	1,139		526	559
Other assets	3,859		3,743	3,734
Accrued liabilities:
Salaries and related	1,177		4,063	1,875
Benefits	3,925		5,001	5,778
Insurance obligations	1,852		1,590	1,426
Warranties	1,639	$ 1,752	3,120	2,456	$ 2,617	$ 2,525
Income Taxes	1,013		536	1,140
Other taxes	977		1,240	1,052
Acquisition-related contingent consideration liability, Current	492		1,375	1,191
Other	831		2,262	2,004
Accrued liabilities	11,906		19,187	16,922
Other liabilities:
Postretirement benefits	7,898		11,812	8,264
Acquisition-related contingent consideration liability, Noncurrent	2,229		3,631	3,587
Deferred income taxes	3,665		7,091	1,406
Uncertain tax positions	3,265		3,259	7,175
Other liabilities	17,057		25,793	20,432
Land [Member]
Property, plant and equipment, net:
Property, plant and equipment	324		11	0
Building and Building Improvements [Member]
Property, plant and equipment, net:
Property, plant and equipment	2,597		1,522	0
Machinery and Equipment [Member]
Property, plant and equipment, net:
Property, plant and equipment	639		0	0
Assets Held-for-sale [Member]
Property, plant and equipment, net:
Accumulated depreciation	(2,207)		(627)	0
Property, plant and equipment, net	1,353		906	0
Land [Member]
Property, plant and equipment, net:
Property, plant and equipment	2,974		3,246	2,077
Building and Building Improvements [Member]
Property, plant and equipment, net:
Property, plant and equipment	76,775		78,140	69,353
Machinery and Equipment [Member]
Property, plant and equipment, net:
Property, plant and equipment	138,921		131,766	124,057
Assets held for use [Member]
Property, plant and equipment, net:
Accumulated depreciation	(102,263)		(96,545)	(95,118)
Property, plant and equipment, net	116,407		116,607	100,369
Assets held for use [Member] | Assets Held-for-sale [Member]
Property, plant and equipment, net:
Property, plant and equipment, net	$ 117,760		$ 117,513	$ 100,369