Schedule of Summarized Financial Data (Parenthetical) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Aug. 31, 2017	Aug. 31, 2016	Aug. 31, 2015
Schedule of Equity Method Investments [Line Items]
Pre-tax goodwill impairment loss	$ 0	$ 0	$ 0
Goodwill	68,590	$ 43,265
GBW Railcar Services LLC
Schedule of Equity Method Investments [Line Items]
Pre-tax goodwill impairment loss	11,200
Goodwill	41,500
Non-cash goodwill impairment	$ 3,500