Annual report pursuant to Section 13 and 15(d)

Income Taxes (Details 2)

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Income Taxes (Details 2)
12 Months Ended
May 31, 2012
May 31, 2011
May 31, 2010
Reconciliation of the U.S. federal statutory tax rate      
Federal statutory tax rate 35.00% 35.00% 35.00%
Increase/(Decrease) resulting from:      
State income taxes, net of federal tax benefit 3.30% 2.50% 2.30%
Tax-exempt municipal bond interest (1.80%) (2.20%) (2.70%)
Other items (0.20%) (0.30%)  
Effective income tax rate 36.30% 35.00% 34.60%