Subsequent Events - Additional Information (Detail) $ in Thousands		1 Months Ended	6 Months Ended
	Apr. 05, 2017 USD ($) Vehicle	Mar. 31, 2017 USD ($)	Feb. 28, 2017 USD ($) Vehicle	Feb. 29, 2016 USD ($)	May 31, 2015
Subsequent Event [Line Items]
Payment for investment | $			$ 550	$ 5,140
Equity method investment, percentage of ownership interest			50.00%
Number of railcars over the next four years | Vehicle			389
Greenbrier-Maxion
Subsequent Event [Line Items]
ownership percentage acquired					19.50%
Subsequent Event | Greenbrier-Maxion
Subsequent Event [Line Items]
Payment for investment | $		$ 20,000
Ownership percentage by parent, before transaction		19.50%
Ownership percentage by parent, after transaction		60.00%
Subsequent Event | Amsted-Maxion Cruzeiro
Subsequent Event [Line Items]
Payment for investment | $		$ 3,250
Ownership percentage by parent, before transaction		19.50%
Ownership percentage by parent, after transaction		24.50%
Ownership percentage, before transaction		80.50%
Ownership percentage, after transaction		40.00%
Subsequent Event | Amsted-Maxion Cruzeiro | Option to increase ownership subject to certain conditions
Subsequent Event [Line Items]
Equity method investment, percentage of ownership interest		29.50%
Subsequent Event | Mitsubishi UFJ Lease & Finance
Subsequent Event [Line Items]
Number of railcars over the next four years | Vehicle	25,000
Purchase of newly manufactured railcars | Vehicle	6,000
Combined transaction value | $	$ 1,000,000
Percentage of ownership held in asset management service entity	50.00%
Number of new and used railcars sold | Vehicle	5,000