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Income Taxes (Schedule of Reconciliation between Income Tax Provision and Statutory Federal Tax Rate) (Details)
12 Months Ended
Apr. 30, 2011
Apr. 30, 2010
Apr. 30, 2009
Income Taxes      
U.S. statutory tax rate 35.00% 35.00% 35.00%
State income taxes, net of federal income tax benefit 4.50% 3.80% 4.20%
Permanent differences (0.30%) (0.50%) 1.60%
Uncertain tax positions 1.10% 0.90% 0.50%
Net decrease in valuation allowance (1.30%) (1.00%) (1.20%)
Other adjustments (0.90%) (0.60%) (1.20%)
Effective tax rate 38.10% 37.60% 38.90%