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Fair Value and Carrying Value of Financial Instruments and Long-Term Debt (Detail) - USD ($) $ in Thousands	Aug. 31, 2016	May 31, 2016	Aug. 31, 2015	May 31, 2015
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents, carrying value	$ 194,470	$ 265,152	$ 169,458	$ 174,711
Marketable equity securities, carrying value	130,543	124,094
Marketable debt securities, carrying value	22,942	22,862
Long-term debt, including current portion, carrying value	1,656,730	1,639,973
Cash and cash equivalents, fair value	194,470	265,152
Marketable securities, fair value	153,485	146,956
Long-term debt, including current portion, fair value	1,965,820	1,925,079
Equity securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities, fair value	130,543	124,094
Fixed maturity
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities, fair value	$ 22,942	$ 22,862