Summary of Significant Accounting Policies - Product Warranty (Details) - USD ($)	12 Months Ended
	Apr. 30, 2015	Apr. 30, 2014	Apr. 30, 2013
Summary Of Significant Accounting Policies - Product Warranty Details
Balance beginning of year	$ 69,000	$ 69,000	$ 79,000
Charges to costs and expenses	11,000	9,000	14,000
Deductions	(70,000)	(9,000)	(24,000)
Balance end of year	$ 10,000	$ 69,000	$ 69,000