Variable Interest Entity - Total assets of EAM, maximum exposure to loss due to involvement with EAM and value of assets and liabilities (Details) (USD $) In Thousands, unless otherwise specified	Jul. 31, 2013		Apr. 30, 2013
Variable Interest Entity [Line Items]
Investment in EAM Trust	$ 57,660		$ 57,511
EAM Trust
Variable Interest Entity [Line Items]
VIE Assets	59,261		59,349
Investment in EAM Trust	57,660	[1]	57,511	[1]
Liabilities
Maximum Exposure to Loss	$ 57,660		$ 57,511

[1] Reported within Long Term Assets on the Consolidated Condensed Balance Sheets.