Fair Value and Carrying Value of Financial Instruments and Long-Term Debt (Detail) - USD ($) $ in Thousands	Aug. 31, 2015	May. 31, 2015	Aug. 31, 2014	May. 31, 2014
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents, carrying value	$ 169,458	$ 174,711	$ 225,025	$ 332,868
Marketable equity securities, carrying value	119,357	131,866
Marketable debt securities, carrying value	22,606	22,904
Long-term debt, including current portion, carrying value	1,732,191	1,656,075
Cash and cash equivalents, fair value	169,458	174,711
Marketable securities, fair value	141,963	154,770
Long-term debt, including current portion, fair value	1,827,275	1,783,962
Equity securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities, fair value	119,357	131,866
Fixed maturity
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities, fair value	$ 22,606	$ 22,904