Selected Balance Sheet Information (Details) (USD $) In Thousands, unless otherwise specified	Apr. 30, 2012	Jan. 31, 2012	Apr. 30, 2011	Jan. 31, 2011
Inventories:
Finished goods	$ 7,688	$ 7,094	$ 7,916
In process	6,847	6,105	5,986
Materials	40,129	41,557	31,636
Inventories	54,664	54,756	45,538
Accrued liabilities:
Salaries and benefits	2,635	4,297	1,972
Vacation	4,584	4,387	3,504
401(k) contributions	555	966	228
Insurance obligations	2,887	2,789	3,134
Profit sharing	413	1,244	354
Warranties	1,792	1,699	1,631	1,437
Acquisition-related contingent consideration	6,658	3,266	266
Other	1,141	1,749	693
Accrued liabilities	20,665	20,397	11,782
Other liabilities:
Postretirement benefits	7,423	7,348	5,774
Acquisition-related contingent consideration	2,169	7,655	2,249
Deferred income taxes	3,944	4,518	102
Uncertain tax positions	5,395	4,946	4,512
Other liabilities	$ 18,931	$ 24,467	$ 12,637