Product Warranty (Schedule Of Warranty Liability) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Jul. 31, 2012	Jul. 31, 2011
Product Warranty [Abstract]
Beginning balance at May 1	$ 1,885	$ 1,738
Accrual	2,257	2,294
Settlements	(2,160)	(2,148)
Ending balance at July 31	$ 1,982	$ 1,884