Derivatives and Hedging-Disclosures and Fair Value Measurements - Offsetting of Financial Assets (Liabilities) and Derivative Assets (Liabilities) (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Sep. 30, 2020
Fair Values Of Financial Assets And Liabilities Including Derivative Financial Instruments [Line Items]
Net Assets (Liabilities) Presented in the Statement of Financial Position		$ (11,437)
Subject to an enforceable master netting arrangement
Fair Values Of Financial Assets And Liabilities Including Derivative Financial Instruments [Line Items]
Gross Assets Recognized	$ 16,328	26,164
Gross Liabilities Offset in the Statement of Financial Position	(4,111)	(37,490)
Net Assets (Liabilities) Presented in the Statement of Financial Position	12,217	(11,326)
Gross Amounts Not Offset in the Statement of Financial Position, Financial Instruments		0
Gross Amounts Not Offset in the Statement of Financial Position, Cash Collateral Received		0
Gross Amounts Not Offset in the Statement of Financial Position, Net Amount	12,217	(11,326)
Subject to an enforceable master netting arrangement \| Fair asset value of derivative instruments
Fair Values Of Financial Assets And Liabilities Including Derivative Financial Instruments [Line Items]
Gross Assets Recognized	15,082
Gross Liabilities Offset in the Statement of Financial Position	(3,666)
Net Assets (Liabilities) Presented in the Statement of Financial Position	11,416
Gross Amounts Not Offset in the Statement of Financial Position, Net Amount	11,416
Subject to an enforceable master netting arrangement \| Other long-term assets, net
Fair Values Of Financial Assets And Liabilities Including Derivative Financial Instruments [Line Items]
Gross Assets Recognized	1,246	1,605
Gross Liabilities Offset in the Statement of Financial Position	(445)	(1,478)
Net Assets (Liabilities) Presented in the Statement of Financial Position	801	127
Gross Amounts Not Offset in the Statement of Financial Position, Financial Instruments		0
Gross Amounts Not Offset in the Statement of Financial Position, Cash Collateral Received		0
Gross Amounts Not Offset in the Statement of Financial Position, Net Amount	$ 801	127
Subject to an enforceable master netting arrangement \| Fair liability and fair asset value of derivative instruments
Fair Values Of Financial Assets And Liabilities Including Derivative Financial Instruments [Line Items]
Gross Assets Recognized		24,274
Gross Liabilities Offset in the Statement of Financial Position		(35,711)
Net Assets (Liabilities) Presented in the Statement of Financial Position		(11,437)
Gross Amounts Not Offset in the Statement of Financial Position, Financial Instruments		0
Gross Amounts Not Offset in the Statement of Financial Position, Cash Collateral Received		0
Gross Amounts Not Offset in the Statement of Financial Position, Net Amount		(11,437)
Subject to an enforceable master netting arrangement \| Other long-term liabilities
Fair Values Of Financial Assets And Liabilities Including Derivative Financial Instruments [Line Items]
Gross Assets Recognized		285
Gross Liabilities Offset in the Statement of Financial Position		(301)
Net Assets (Liabilities) Presented in the Statement of Financial Position		(16)
Gross Amounts Not Offset in the Statement of Financial Position, Financial Instruments		0
Gross Amounts Not Offset in the Statement of Financial Position, Cash Collateral Received		0
Gross Amounts Not Offset in the Statement of Financial Position, Net Amount		$ (16)

Cash collateral received from not offset against derivative assets and liabilities.

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