Commitments and Contingencies (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Apr. 30, 2015	Apr. 30, 2014	Apr. 30, 2013
Commitments And Contingencies [Line Items]
Warranty claims, period from original ship date	2 months
Total rental expenses	$ 8.8	$ 8.0	$ 7.4
Significant Shareholders [Member]
Commitments And Contingencies [Line Items]
Rent agreement term	5 years
Reltaed party rent expense	$ 0.5	$ 0.5	$ 0.5
Rent expense from remaining term	$ 0.4