Investments - Narrative (Details) - USD ($)	3 Months Ended	12 Months Ended
	Aug. 31, 2014	May 31, 2016	May 31, 2015	May 31, 2014
Investments [Abstract]
Investments		$ 124,952,000	$ 329,692,000
Cash surrender value of life insurance policies		108,100,000	101,800,000
Equity method investments		14,500,000	225,700,000
Cost method investments		2,400,000	2,200,000
Dividends received on equity method investment		0	5,247,000	$ 0
Cash received from sale of equity method investment			35,200,000
Gain on sale of stock of an equity method investment, net of tax	$ 13,600,000		13,600,000
Losses due to impairment		$ 0	$ 0	$ 0