Consolidated Condensed Statements of Comprehensive Income (Unaudited) (Parenthetical) (USD $)	3 Months Ended		6 Months Ended
	Nov. 30, 2013	Nov. 30, 2012	Nov. 30, 2013	Nov. 30, 2012
Change in fair value of derivative, tax expense (net of less than $0.1 million)	$ 100,000		$ 100,000	$ 100,000
Amortization of interest rate lock agreements, tax expense (benefit)	(295,000)	(300,000)	(589,000)	(600,000)
Change in fair value of available-for-sale securities, tax expense (benefit) (net of less than $0.1 million)	$ 100,000	$ (100,000)	$ 100,000	$ (100,000)