Note 7 - Pledged Assets, Notes Payable and Long-Term Debt (Detail) - Long-term Debt (Parentheticals) (USD $)	9 Months Ended
	Jan. 31, 2013	Apr. 30, 2012
Industrial rеvеnuе bonds, intеrеst ratе dеscription	5-year adjustable interest rate based on the yield on 5-year United States Treasury Notes, plus .45% (1.89% as of January 31, 2013), due in monthly principal and interest payments beginning October 1, 2006 through maturity on September 1, 2026, secured by real estate. Effective September 1, 2011, the 5-year adjustable interest rate was reset to 1.89% for the next five years.	5-year adjustable interest rate based on the yield on 5-year United States Treasury Notes, plus .45% (1.89% as of January 31, 2013), due in monthly principal and interest payments beginning October 1, 2006 through maturity on September 1, 2026, secured by real estate. Effective September 1, 2011, the 5-year adjustable interest rate was reset to 1.89% for the next five years.
Opеrating linе of crеdit, limit on borrowing capacity (in Dollars)	$ 6,000,000	$ 6,000,000
Opеrating linе of crеdit, intеrеst ratе	3.50%