Investments - Components of assets and liabilities (Details 3) (USD $) In Thousands, unless otherwise specified	Jan. 31, 2013		Apr. 30, 2012
Schedule of Equity Method Investments [Line Items]
Total assets	$ 83,334		$ 84,369
Total liabilities	50,477		52,055
EAM Trust
Schedule of Equity Method Investments [Line Items]
Total assets	59,141		57,482
Total liabilities	(2,664)	[1]	(663)	[1]
Total equity	$ 56,477		$ 56,819

[1] At January 31, 2013, EAM's total liabilities included a payable to VLI for its accrued non-voting revenues and non-voting profits interests of $1,588,000.