Assets Measured at Fair Value on Non-recurring Basis (Detail) - USD ($)		Feb. 29, 2016	Nov. 30, 2015	May. 31, 2015
Fair Value [Line Items]
Asset measured at fair value on nonrecurring basis		$ 0		$ 12,403,000
Long-lived Assets Held and Used
Fair Value [Line Items]
Asset measured at fair value on nonrecurring basis			$ 36,933,000	12,403,000	[1]
Significant Unobservable Inputs (Level 3)
Fair Value [Line Items]
Asset measured at fair value on nonrecurring basis				12,403,000
Significant Unobservable Inputs (Level 3) | Long-lived Assets Held and Used
Fair Value [Line Items]
Asset measured at fair value on nonrecurring basis	[1]			$ 12,403,000

[1] During the fourth quarter of fiscal 2015, management reviewed certain intangible assets related to our CNG fuel systems joint venture, dHybrid, for impairment. In accordance with the applicable accounting guidance, the intangible assets were written down to their fair value of $600,000, resulting in an impairment charge of $2,344,000. The key assumptions that drove the fair value calculation were projected cash flows and the discount rate.