Summary of Significant Accounting Policies - Product Warranty (Details) - USD ($)	12 Months Ended
	Apr. 30, 2016	Apr. 30, 2015
Accounting Policies [Abstract]
Balance beginning of year	$ 10,000	$ 69,000
Charges to costs and expenses	0	11,000
Deductions	0	(70,000)
Balance end of year	$ 10,000	$ 10,000