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Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands		12 Months Ended
	Sep. 01, 2018	Aug. 31, 2018	Aug. 31, 2017	Aug. 31, 2016	Aug. 02, 2018	Jun. 30, 2017	Jun. 01, 2017	Oct. 31, 2016	Aug. 31, 2015
Summary Of Significant Accounting Policies [Line Items]
Net foreign currency translation adjustment		$ 21,500	$ 5,400	$ 20,800
Allowance for doubtful accounts		2,701	1,768	2,215					$ 2,449
Leased railcars for syndication		$ 130,926	91,272
Property, Plant and Equipment useful life		35 years
Goodwill impairment		$ 0	0	0
Percentage of revenue and gross margin		40.00%
Deferred revenue		$ 105,954	129,260
Retained risk threshold percentage		10.00%
Research and development		$ 6,000	4,200	2,700
Stock based compensation expense		$ 29,314	$ 26,427	$ 24,037
Performance based share based compensation		317,036	269,705	447,895
Share based compensation, non vested shares		467,710
Unamortized share based compensation		$ 15,500
Greenbrier-Astra Rail
Summary Of Significant Accounting Policies [Line Items]
Interest in joint venture							25.00%
Ownership percentage by parent			75.00%				75.00%
GIMSA
Summary Of Significant Accounting Policies [Line Items]
Interest in joint venture								50.00%
Rayvag
Summary Of Significant Accounting Policies [Line Items]
Interest in joint venture		68.00%			68.00%
Summit Railroad Products, Inc
Summary Of Significant Accounting Policies [Line Items]
Interest in joint venture		50.00%
Accounting Standards Update 2014-09 \| Subsequent Event
Summary Of Significant Accounting Policies [Line Items]
Increase to retained earnings	$ 5,400
Reclassification from accrued maintenance to contract liabilities	$ 2,400
Phantom Stock Units (PSUs)
Summary Of Significant Accounting Policies [Line Items]
Performance based share based compensation		0	151,634	268,161
Share based compensation, non vested shares		200,686
Additional shares available for grant if performance-based phantom stock units vest at stretch level of performance		200,686
Share based compensation, fair value of phantom stock			$ 6,700	$ 7,900
Stock compensation expenses		$ 12,100	6,200	1,500
Unamortized share based compensation		$ 5,900	$ 10,900	$ 7,500
Greenbrier
Summary Of Significant Accounting Policies [Line Items]
Percentage of ownership in entity		40.00%				40.00%
Upfront Fee [Member]
Summary Of Significant Accounting Policies [Line Items]
Unrecognized deferred revenue		$ 40,000
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