Investments - Components of EAM's investment management operations (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended				6 Months Ended
	Oct. 31, 2012		Oct. 31, 2011		Oct. 31, 2012		Oct. 31, 2011
Schedule of Equity Method Investments [Line Items]
Value Line's non-voting revenues interest					$ 2,808		$ 2,821
Net income	1,572		1,915		3,348		3,991
EAM Trust
Schedule of Equity Method Investments [Line Items]
Investment management fees earned from the Value Line Funds, net of waivers shown below	3,149		2,957		6,229		6,258
12b-1 fees, net of waivers shown below	985		822		1,876		1,750
Other income			5				9
Investment management fee waivers (1)	167	[1]	227	[1]	346	[1]	457	[1]
12b-1 fees waivers (1)	547	[1]	548	[1]	1,088	[1]	1,166	[1]
Value Line's non-voting revenues interest	1,414		1,330		2,808		2,821
Net income	$ 230	[2]	$ 26	[2]	$ 388	[2]	$ 188	[2]

[1] For the six months ended October 31, 2012, investment management fee waivers primarily related to the U.S. Government Money Market Fund ("USGMMF") and the 12b-1 fee waivers related to nine of the Value Line Mutual Funds. For the six months ended October 31, 2011, investment management fee waivers primarily related to the USGMMF and the 12b-1 fee waivers related to eleven of the Value Line Mutual Funds.

[2] Represents EAM's net income, after giving effect to Value Line's non-voting revenues interest, but before distributions to voting profits interest holders and to the Company in respect of its 50% non-voting profits interest.