Income Taxes - Reconciliation of Income Tax Expense Using the Statutory Rate and Actual Income Tax Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	May. 31, 2015	May. 31, 2014	May. 31, 2013
Reconciliation of income tax expense for continuing operations using the statutory rate and actual income tax expense is as follows:
Income taxes at the U.S. federal statutory rate	$ 227,316	$ 212,464	$ 175,237
State and local income taxes, net of federal benefit	16,623	20,252	12,211
Other	(2,543)	41	(3,359)
Income taxes	$ 241,396	$ 232,757	$ 184,089