Summary of Significant Accounting Policies - Product Warranty (Details) (USD $)	12 Months Ended
	Apr. 30, 2014	Apr. 30, 2013	Apr. 30, 2012
Summary Of Significant Accounting Policies - Product Warranty Details
Balance beginning of year	$ 69,000	$ 79,000	$ 79,000
Charges to costs and expenses	9,000	14,000	6,000
Deductions	(9,000)	(24,000)	(6,000)
Balance end of year	$ 69,000	$ 69,000	$ 79,000