Restructuring Charges (Narrative) (Details) (USD $)	3 Months Ended			9 Months Ended		12 Months Ended
	Jan. 31, 2015	Jan. 31, 2014	Jan. 31, 2012 manufacturing_plant	Jan. 31, 2015	Jan. 31, 2014	Apr. 30, 2014	Apr. 30, 2013	Apr. 30, 2012
Restructuring Cost and Reserve [Line Items]
Plants committed to close			2
Pre-tax restructuring charges	$ 3,000	$ 48,000		$ 6,000	$ 161,000
Recognized recurring operating costs for closed facilities				52,000
Net book value of plants recoverable	1,000,000			1,000,000
2012 Restructuring Plan [Member]
Restructuring Cost and Reserve [Line Items]
Pre-tax restructuring charges				$ 6,000		$ 17,100,000	$ 17,100,000	$ 17,100,000
Number of manufacturing plants held for sale				1