Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Aug. 31, 2017	Aug. 31, 2016	Aug. 31, 2015	Jun. 30, 2017	Jun. 01, 2017	May 31, 2017	Apr. 30, 2017	Aug. 31, 2014	Oct. 31, 2006
Summary Of Significant Accounting Policies [Line Items]
Net foreign currency translation adjustment	$ 5,400	$ 20,800	$ 18,700
Allowance for doubtful accounts	1,768	2,215	2,449					$ 2,033
Leased railcars for syndication	$ 91,272	144,932
Property, Plant and Equipment useful life	35 years
Equity method investment, percentage of ownership interest	50.00%
Goodwill impairment	$ 0	0	0
Percentage of revenue and gross margin	40.00%
Deferred revenue	$ 129,260	95,721
Retained risk threshold percentage	10.00%
Research and development	$ 4,200	2,700	2,500
Stock based compensation expense	$ 26,427	$ 24,037	$ 19,459
Performance based share based compensation	269,705	447,895	402,196
Share based compensation, non vested shares	492,886
Unamortized share based compensation	$ 14,100
Intangibles and other assets, net	85,177	$ 67,359
Notes payable	$ 558,228	301,853
Greenbrier-Astra Rail
Summary Of Significant Accounting Policies [Line Items]
Ownership percentage by parent	75.00%				75.00%
Interest in joint venture					25.00%
GIMSA
Summary Of Significant Accounting Policies [Line Items]
Interest in joint venture									50.00%
Accounting Standards Update 2015-03 | Reclassifications
Summary Of Significant Accounting Policies [Line Items]
Intangibles and other assets, net		(2,100)
Notes payable		$ 2,100
Phantom Stock Units (PSUs)
Summary Of Significant Accounting Policies [Line Items]
Performance based share based compensation	151,634	268,161
Share based compensation, non vested shares	203,768
Additional shares available for grant if performance-based phantom stock units vest at stretch level of performance	203,768
Share based compensation, fair value of phantom stock	$ 6,700	$ 7,900
Stock compensation expenses	6,200	1,500
Unamortized share based compensation	$ 10,900	$ 7,500
Greenbrier
Summary Of Significant Accounting Policies [Line Items]
Equity method investment, percentage of ownership interest	40.00%			40.00%
Upfront Fee [Member]
Summary Of Significant Accounting Policies [Line Items]
Unrecognized deferred revenue	$ 40,000
GBW Railcar Services LLC
Summary Of Significant Accounting Policies [Line Items]
Equity method investment, percentage of ownership interest	50.00%		50.00%
Goodwill impairment	$ 11,200
Ohio Castings Company LLC
Summary Of Significant Accounting Policies [Line Items]
Equity method investment, percentage of ownership interest	33.00%
Greenbrier-Maxion
Summary Of Significant Accounting Policies [Line Items]
Equity method investment, percentage of ownership interest	60.00%					60.00%	19.50%
Greenbrier-Maxion | BRAZIL
Summary Of Significant Accounting Policies [Line Items]
Ownership percentage by parent	40.00%
Amsted-Maxion Cruzeiro
Summary Of Significant Accounting Policies [Line Items]
Equity method investment, percentage of ownership interest	24.50%					24.50%	19.50%
GGSynergy SA de C.V.
Summary Of Significant Accounting Policies [Line Items]
Equity method investment, percentage of ownership interest	50.00%
MUL Greenbrier LLC
Summary Of Significant Accounting Policies [Line Items]
Equity method investment, percentage of ownership interest	8.00%
Green Union One Trust
Summary Of Significant Accounting Policies [Line Items]
Equity method investment, percentage of ownership interest	1.00%
Green Union Two Trust
Summary Of Significant Accounting Policies [Line Items]
Equity method investment, percentage of ownership interest	1.00%
Green Union Three Trust
Summary Of Significant Accounting Policies [Line Items]
Equity method investment, percentage of ownership interest	1.00%
Greenbrier Railcar Funding I LLC
Summary Of Significant Accounting Policies [Line Items]
Equity method investment, percentage of ownership interest	40.00%
Customer Relationships | Minimum
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives	5 years
Customer Relationships | Maximum
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives	20 years