Assets Measured at Fair Value on Non-recurring Basis (Parenthetical) (Detail) - USD ($)	3 Months Ended													12 Months Ended
	Nov. 30, 2015	[1]	Aug. 31, 2015		May 31, 2015		Feb. 28, 2015		Nov. 30, 2014		Aug. 31, 2014	[1]	Nov. 30, 2013	May 31, 2016	May 31, 2015	May 31, 2014
Fair Value [Line Items]
Impairment of long-lived assets	$ 22,962,000		$ 3,000,000	[1]	$ 2,344,000	[1]	$ 81,600,000	[1]	$ 14,235,000	[1]	$ 1,950,000		$ 30,734,000	$ 25,962,000	$ 100,129,000	$ 58,246,000
Assets fair value					12,403,000									0	12,403,000
DHybrid Systems LLC
Fair Value [Line Items]
Impairment of long-lived assets					2,344,000
Assets fair value					$ 600,000										600,000
Engineered Cabs
Fair Value [Line Items]
Impairment of long-lived assets			$ 3,000,000						$ 2,389,000					$ 3,000,000	$ 83,989,000	$ 19,100,000
Engineered Cabs | Customer relationships
Fair Value [Line Items]
Impairment of long-lived assets							22,356,000
Assets fair value							2,000,000
Engineered Cabs | Florence Facility
Fair Value [Line Items]
Impairment of long-lived assets							14,311,000
Assets fair value							$ 9,803,000

[1] For additional information regarding the Company's impairment charges, refer to "Note C - Goodwill and Other Long-Lived Assets."