Related Party Transactions - Income from its non-voting revenues interest and its non-voting profits interests in EAM (Details) - USD ($) $ in Thousands	12 Months Ended
	Apr. 30, 2015	Apr. 30, 2014	Apr. 30, 2013
Related Party Transactions [Abstract]
Non-voting revenues interest in EAM	$ 7,346	$ 6,767	$ 5,781
Non-voting profits interest in EAM	624	732	479
Revenues and profits interests in EAM Trust	$ 7,970	$ 7,499	$ 6,260