Amounts Reclassified out of Accumulated Other Comprehensive Loss (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended	6 Months Ended
Feb. 28, 2015	Feb. 28, 2014	Feb. 28, 2015	Feb. 28, 2014
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Revenue	$ 630,149us-gaap_Revenues	$ 502,216us-gaap_Revenues	$ 1,125,207us-gaap_Revenues	$ 992,571us-gaap_Revenues
Interest and foreign exchange	(1,929)gbx_InterestAndForeignExchange	(4,099)gbx_InterestAndForeignExchange	(5,070)gbx_InterestAndForeignExchange	(8,843)gbx_InterestAndForeignExchange
Earnings before income taxes and earnings (loss) from unconsolidated affiliates	90,603	30,503	141,884	63,981
Tax expense	(29,372)us-gaap_IncomeTaxExpenseBenefit	(9,883)us-gaap_IncomeTaxExpenseBenefit	(45,426)us-gaap_IncomeTaxExpenseBenefit	(20,405)us-gaap_IncomeTaxExpenseBenefit
Net of tax	61,231	20,620	96,458	43,576
Unrealized Losses on Derivative Financial Instruments \| Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Earnings before income taxes and earnings (loss) from unconsolidated affiliates	577	320	1,041	589
Tax expense	(195)	(140)	(370)	(272)
Net of tax	382	180	671	317
Unrealized Losses on Derivative Financial Instruments \| Reclassification out of Accumulated Other Comprehensive Income \| Foreign Exchange Contracts
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Revenue	127	(89)	134	(240)
Unrealized Losses on Derivative Financial Instruments \| Reclassification out of Accumulated Other Comprehensive Income \| Interest rate swap contracts
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Interest and foreign exchange	$ 450	$ 409	$ 907	$ 829

Interest and foreign exchange

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- Definition

Sum of operating profit and nonoperating income or expense before Income or Loss from equity method investments, income taxes, extraordinary items, and noncontrolling interest.

+ References

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- Definition

This element represents the income or loss from continuing operations attributable to the economic entity which may also be defined as revenue less expenses and taxes from ongoing operations before extraordinary items, and noncontrolling interest.

+ References

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 810

-SubTopic 10

-Section 45

-Paragraph 19

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- Definition

Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 235

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.4-08.(h))

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-Name Regulation S-X (SX)

-Number 210

-Section 08

-Paragraph h

-Article 4

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-Publisher FASB

-Name Accounting Standards Codification

-Glossary Income Tax Expense (or Benefit)

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section 50

-Paragraph 9

-Subparagraph (a),(b)

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- Definition

Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

+ References

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.1)

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 1

-Article 5

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