Impairment of Long-Lived Assets - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Aug. 31, 2016	Aug. 31, 2015
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment of long-lived assets	$ 0	$ 3,000
Engineered Cabs
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment of long-lived assets		3,000
Engineered Cabs | Long-lived Assets Held and Used
Impaired Long-Lived Assets Held and Used [Line Items]
Carrying value long-lived assets		4,059
Asset measured at fair value on nonrecurring basis		$ 1,059