Investments in Unconsolidated Affiliates - Schedule of Summarized Financial Data (Parenthetical) (Detail) - USD ($) $ in Thousands	12 Months Ended
Aug. 31, 2018	Aug. 31, 2017	Aug. 31, 2016	Aug. 20, 2018
Schedule of Equity Method Investments [Line Items]
Pre-tax goodwill impairment loss	$ 0	$ 0	$ 0
Goodwill	78,211	68,590
GBW Railcar Services LLC
Schedule of Equity Method Investments [Line Items]
Pre-tax goodwill impairment loss	26,400	$ 11,200
Goodwill	$ 7,863			$ 15,100

Amount of loss from the write-down of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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