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Related Party Transactions - Income from non-voting revenues interest and non-voting profits interests in EAM (Details) - USD ($)
$ in Thousands
 3 Months Ended
Jul. 31, 2015
Jul. 31, 2014
Related Party Transactions [Abstract]    
Non-voting revenues interest in EAM $ 1,902 $ 1,833
Non-voting profits interest in EAM 140 189
Non-voting revenues and non-voting profits interests in EAM Trust $ 2,042 $ 2,022