Related Party Transactions - Income from its non-voting revenues interest and its non-voting profits interests in EAM (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Jul. 31, 2013	Jul. 31, 2012
Related Party Transactions [Abstract]
Non-voting revenues interest in EAM	$ 1,598	$ 1,394
Non-voting profits interest in EAM	171	79
Revenues and profits interests in EAM Trust	$ 1,769	$ 1,473