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, 2015
May. 31, 2014
May. 31, 2013
Income Tax Disclosure [Abstract]      
Federal statutory tax rate 35.00% 35.00% 35.00%
Increase/(decrease) resulting from:      
State income taxes, net of federal tax benefit 3.00% 3.30% 3.00%
Tax settlement 0.00% 0.00% 1.50%
Tax-exempt municipal bond interest (1.50%) (1.50%) (1.70%)
Other items (0.20%) (0.30%) (0.20%)
Effective income tax rate 36.30% 36.50% 37.60%