Segment Information - Additional Information (Detail)	Aug. 20, 2018 Facility Segment	Aug. 19, 2018 Segment	Aug. 31, 2018	Aug. 31, 2015
Segment Reporting Information [Line Items]
Number of reportable segments | Segment	3	4
Number of railcars repair shops returned to business | Facility	12
GBW Railcar Services LLC
Segment Reporting Information [Line Items]
Equity method investment, percentage of ownership interest	50.00%		50.00%	50.00%