Variable Interest Entity - Total assets of EAM, maximum exposure to loss due to involvement with EAM and value of the assets and liabilities (Details) (USD $) In Thousands, unless otherwise specified	Apr. 30, 2013		Apr. 30, 2012
Variable Interest Entity [Line Items]
Investment in EAM Trust	$ 57,511		$ 56,331
EAM Trust
Variable Interest Entity [Line Items]
VIE Assets	59,349		57,482
Investment in EAM Trust	57,511	[1]	56,331	[1]
Liabilities
Maximum Exposure to Loss	$ 57,511		$ 56,331

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