Other Property - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	May. 31, 2015	May. 31, 2014	May. 31, 2013
Property, Plant and Equipment [Line Items]
Depreciation expense	$ 56,445	$ 57,034	$ 56,795
Property, Plant and Equipment, Other Types [Member]
Property, Plant and Equipment [Line Items]
Depreciation expense	$ 987	$ 1,089	$ 1,149