Restructuring Charges (Narrative) (Details) (USD $)	12 Months Ended				3 Months Ended	12 Months Ended
	Apr. 30, 2013	Apr. 30, 2012	Apr. 30, 2011	Apr. 30, 2009 2009 Restructuring Plan[Member] segment	Jan. 31, 2012 2012 Restructuring Plan [Member] segment	Apr. 30, 2013 2012 Restructuring Plan [Member] segment	Apr. 30, 2012 2012 Restructuring Plan [Member]	Apr. 30, 2013 2012 Restructuring Plan [Member] Facilities-Related [Member]	Apr. 30, 2013 2012 Restructuring Plan [Member] Building Impairment [Member]	Apr. 30, 2013 2012 Restructuring Plan [Member] Severance And Separations Costs [Member]	Apr. 30, 2013 2012 Restructuring Plan [Member] Professional Fees [Member]	Apr. 30, 2013 2012 And 2009 Restructuring Plan [Member]	Apr. 30, 2012 2012 And 2009 Restructuring Plan [Member]	Apr. 30, 2011 2012 And 2009 Restructuring Plan [Member]
Restructuring Cost and Reserve [Line Items]
Plants committed to close				2	2
Number of manufacturing plants held for sale						2
Pre-tax restructuring charges	$ 1,433,000	$ 16,321,000	$ 62,000			$ 1,400,000	$ 15,900,000	$ 700,000	$ 300,000	$ 200,000	$ 200,000	$ 1,400,000	$ 16,300,000	$ 62,000
Reserve for restructuring charges	13,000	2,817,000
Impairment charge relating to plants included as held for sale	300,000
Net book value of plants recoverable	2,700,000
Recognized recurring operating costs for closed facilities						900,000
Recognized gain from sale of plant	$ 300,000