Investments - Narrative (Details) - USD ($)		3 Months Ended
	Jun. 30, 2014	Aug. 31, 2015	Aug. 31, 2014	May. 31, 2015
Investments, Debt and Equity Securities [Abstract]
Investments		$ 123,494,000		$ 329,692,000
Equity method investments		14,600,000		225,700,000
Cash surrender value of insurance policies		106,700,000		101,800,000
Cost method investments		2,200,000		$ 2,200,000
Dividends received on equity method investment	$ 5,200,000	0	$ 5,247,000
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
Losses due to impairment		$ 0	$ 0