Convertible debt retired.

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Debt instrument maturity month and year.

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Loss on extinguishment of debt.

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Adjustment to additional paid in capital resulting from the recognition of convertible debt instruments as two separate components - a debt component and an equity component. This bifurcation may result in a basis difference associated with the liability component that represents a temporary difference for purposes of applying accounting for income taxes. The initial recognition of deferred taxes for the tax effect of that temporary difference is as an adjustment to additional paid in capital.

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Value of input used to measure alternative investment.

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Aggregate number of common shares reserved for future issuance.

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Fair value portion of borrowing which can be exchanged for a specified number of another security at the option of the issuer or the holder, for example, but not limited to, the entity's common stock.

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The value of the financial instrument(s) that the original debt is being converted into in a noncash (or part noncash) transaction. "Part noncash" refers to that portion of the transaction not resulting in cash receipts or cash payments in the period.

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Percentage points added to the reference rate to compute the variable rate on the debt instrument.

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Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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The carrying amount of the equity component of convertible debt which may be settled in cash upon conversion.

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The price per share of the conversion feature embedded in the debt instrument.

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Ratio applied to the conversion of debt instrument into equity with equity shares divided by debt principal amount.

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Latest date when the debt instrument can be converted into equity, in YYYY-MM-DD format.

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Minimum percentage of common stock price to conversion price of convertible debt instruments to determine eligibility of conversion.

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Face (par) amount of debt instrument at time of issuance.

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Contractual interest rate for funds borrowed, under the debt agreement.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Date when the debt instrument is scheduled to be fully repaid, in YYYY-MM-DD format.

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Amount of the required periodic payments applied to principal.

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Amount of payment greater than the preceding installment payments to be paid at final maturity date of debt.

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Description of debt redemption features under terms of the debt agreement.

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End date of debt instrument redemption period, in YYYY-MM-DD format.

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Start date of debt instrument redemption period, in YYYY-MM-DD format.

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Amount, after accumulated amortization, of debt discount.

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Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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Fixed interest rate related to the interest rate derivative.

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Description of long-term debt arrangements, which are debt arrangements that originally require full repayment more than twelve months after issuance or greater than the normal operating cycle of the company, if longer, and disclosures pertaining to the underlying arrangements, including repayment terms, conversion features, interest rates, restrictions on assets and activities, debt covenants, and other matters important to users of the financial statements. Types of long-term debt arrangements include borrowing under notes payable, bonds payable, debentures, term loans, and other contractual obligations for payment.

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Including the current and noncurrent portions, carrying value as of the balance sheet date of uncollateralized debt obligations (with maturities initially due after one year or beyond the operating cycle if longer).

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Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=gbx_TwoPointTwoFiveConvertibleSeniorNotesDue2024Member
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Data Type:	na
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Period Type:

Notes Payable, Net - Additional Information (Detail) - USD ($) $ / shares in Units, shares in Millions	1 Months Ended	12 Months Ended
	Apr. 30, 2021	Aug. 31, 2021	Aug. 31, 2020	Aug. 31, 2019
Debt Instrument [Line Items]
Debt instrument amount outstanding		$ 915,525,000	$ 833,993,000
Debt issuance costs		8,597,000	$ 3,623,000
Loss on extinguishment of debt		5,800,000
Other Term Loan Due September 2022
Debt Instrument [Line Items]
Senior term debt		400,000
Other Term Loan Due January 2022 to April 2026
Debt Instrument [Line Items]
Unsecured debt		1,700,000
2026 Term Loan
Debt Instrument [Line Items]
Senior term debt		$ 291,900,000
Debt instrument, maturity month and year		2026-08
Periodic Principal Payment		$ 3,650,000
Balloon payment		$ 222,600,000
Swap agreement interest rate		50.00%
Fixed interest rate		3.19%
Debt instrument amount outstanding		$ 291,900,000
2026 Term Loan \| LIBOR
Debt Instrument [Line Items]
Debt instrument, percentage points added to the reference rate		1.50%
2027 Term Loan
Debt Instrument [Line Items]
Senior term debt		$ 200,000,000.0
Debt instrument, maturity month and year		2027-08
Periodic Principal Payment		$ 1,750,000
Balloon payment		$ 158,000,000.0
Swap agreement interest rate		50.00%
Fixed interest rate		4.62%
Debt instrument amount outstanding		$ 200,000,000.0
2027 Term Loan \| LIBOR
Debt Instrument [Line Items]
Debt instrument, percentage points added to the reference rate		1.625%
2.875% Convertible senior notes, due 2028
Debt Instrument [Line Items]
Proceeds from convertible senior notes	$ 373,800,000
Debt instrument, interest rate	2.875%	2.875%
Description of long term debt		These interest payments are payable semiannually in arrears on April 15 and October 15, commencing October 15, 2021.
Frequency of payments		semiannually
Debt instrument, maturity date		Apr. 15, 2028
Convertible notes initial conversion rate, shares per $1,000 principal amount		0.180317
Debt instrument, convertible, principal amount		$ 1,000
Convertible notes conversion rate, per share		$ 55.46
Initial debt discount		$ 73,600,000
Debt issuance costs		$ 12,000,000.0
Number of shares reserved for future issuance		8.8
2.875% Convertible senior notes, due 2028 \| Redemption on or After April 15, 2025
Debt Instrument [Line Items]
Debt instrument, convertible, latest date		Jan. 15, 2028
Debt instrument redemption start date		Apr. 15, 2025
Debt instrument redemption end date		Apr. 15, 2028
Debt instrument, convertible, threshold percentage of stock price trigger		130.00%
Debt instrument redemption description		Additionally, the Company may elect to call the notes on or after April 15, 2025 and on or before the 40th trading day prior to April 15, 2028, at a cash redemption price described in the 2028 Notes Indenture if the stock price exceeds 130% of the conversion price during certain trading days as defined in the 2028 Notes Indenture.
2.875% Convertible senior notes, due 2028 \| ASC 470-20
Debt Instrument [Line Items]
Proceeds from convertible senior notes		$ 373,800,000
Convertible notes, fair value		300,200,000
Convertible notes, equity component		73,600,000
2.875% Convertible senior notes, due 2028 \| ASC 470-20 \| Additional Paid-in Capital
Debt Instrument [Line Items]
Convertible Senior Notes, equity component, net of tax		$ 17,300,000
2.875% Convertible senior notes, due 2028 \| ASC 470-20 \| Measurement Input, Risk Free Interest Rate
Debt Instrument [Line Items]
Fair value assumed, interest rate		0.0575
2.875% Convertible senior notes, due 2024
Debt Instrument [Line Items]
Debt instrument, interest rate		2.875%	2.875%	2.875%
Description of long term debt		Convertible senior notes, due 2024, bear interest at a fixed rate of 2.875%, paid semi-annually in arrears on February 1st and August 1st.
Frequency of payments		semi-annually
Debt instrument, maturity date		Feb. 01, 2024
Convertible notes initial conversion rate, shares per $1,000 principal amount		0.166234
Debt instrument, convertible, principal amount		$ 1,000
Convertible notes conversion rate, per share		$ 60.16
Initial debt discount		$ 33,100,000
Debt issuance costs		$ 8,000,000.0
Number of shares reserved for future issuance		1.0
Convertible debt retired		$ 227,300,000
2.875% Convertible senior notes, due 2024 \| ASC 470-20
Debt Instrument [Line Items]
Proceeds from convertible senior notes		275,000,000
Convertible notes, fair value		241,900,000
Convertible notes, equity component		$ 2,600,000	$ 33,100,000
2.875% Convertible senior notes, due 2024 \| ASC 470-20 \| Measurement Input, Risk Free Interest Rate
Debt Instrument [Line Items]
Fair value assumed, interest rate		0.05
2.25% Convertible senior notes, due 2024
Debt Instrument [Line Items]
Debt instrument, interest rate		2.25%	2.25%	2.25%